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In [[mathematics]], '''Sobolev spaces for planar domains''' are one of the principal techniques used in the theory of [[partial differential equation]]s for solving the [[Dirichlet boundary condition|Dirichlet]] and [[Neumann boundary condition|Neumann]] boundary value problems for the Laplacian in a bounded domain in the plane with smooth boundary. The methods use the theory of [[bounded operator]]s on [[Hilbert space]]. They can be used to deduce regularity properties of solutions and to solve the corresponding eigenvalue problems. | |||
==Sobolev spaces with boundary conditions== | |||
Let Ω be a bounded domain in '''R'''<sup>2</sup> with smooth boundary. Since Ω is contained in a large square in '''R'''<sup>2</sup>, it can be regarded as a domain in '''T'''<sup>2</sup> by identifying opposite sides of the square. The theory of Sobolev spaces on '''T'''<sup>2</sup> can be found in {{harvtxt|Bers|John|Schechter|1979}}, an account which is followed in several later textbooks such as {{harvtxt|Warner|1983}} and {{harvtxt|Griffiths|Harris|1994}}. | |||
For ''k'' an integer, the (restricted) '''Sobolev space''' H<sup>''k''</sup><sub>0</sub>(Ω) is defined as the closure of C<sup>∞</sup><sub>''c''</sub>(Ω) in the standard [[Sobolev space]] H<sup>''k</sup>('''T'''<sup>2</sup>). | |||
*For ''k'' = 0, H<sup>0</sup><sub>0</sub>(Ω) equals L<sup>2</sup>(Ω). | |||
*'''Vanishing properties on boundary:''' For ''k'' > 0 the elements of H<sup>''k''</sup><sub>0</sub>(Ω) are referred to as "L<sup>2</sup> functions on Ω which vanish with their first ''k'' − 1 derivatives on the boundary."<ref>{{harvnb|Bers|John|Schechter|1979|pp=192–193}}</ref> In fact if | |||
::<math>\displaystyle{f \in C^k(\overline{\Omega})}</math> | |||
:agrees with a function in H<sup>''k''</sup><sub>0</sub>(Ω), then ''g'' = ∂<sup>α</sup> ''f'' is in C<sup>1</sup>. Let ''f''<sub>''n''</sub> be smooth functions of compact support in Ω tending to ''f'' in the Sobolev norm and set ''g''<sub>''n''</sub> = ∂<sup>α</sup> ''f''<sub>''n''</sub>. Thus ''g''<sub>''n''</sub> tends towards ''g'' in H<sup>1</sup><sub>0</sub>(Ω). Hence for ''h'' in C<sup>∞</sup>('''T'''<sup>2</sup>) and ''D'' = ''a'' ∂<sub>''x''</sub> +b ∂<sub>''y''</sub>, | |||
::<math>\displaystyle{\iint_\Omega g (Dh) + (Dg) h \, dx dy =\lim_{n\rightarrow 0}\iint_\Omega g (Dh_n) + (Dg) h_n \, dx dy =0.}</math> | |||
:By [[Green's theorem]] this implies | |||
::<math>\displaystyle{\int_{\partial\Omega} gk =0,}</math> | |||
:where ''k'' = ''h'' cos '''n''' ⋅ (''a'',''b'') with '''n''' the unit normal to the boundary. Since such ''k'' form a dense subspace of L<sup>2</sup>(Ω), it follows that ''g'' = 0 on the boundary. | |||
*'''Support properties:''' Let Ω<sup>''c''</sup> be the complement of the closure of Ω and define restricted Sobolev spaces analogously for Ω<sup>''c''</sup>. Both sets of spaces have a natural pairing with C<sup>∞</sup>('''T'''<sup>2</sup>). The Sobolev space for Ω is the annihilator in the Sobolev space for '''T'''<sup>2</sup> of C<sup>∞</sup><sub>''c''</sub>(Ω<sup>''c''</sup>) and that for Ω<sup>''c''</sup> is the annihilator of C<sup>∞</sup><sub>''c''</sub>(Ω).<ref>{{harvnb|Chazarain|Piriou|1982}}</ref> In fact this is proved by locally applying a small translation to move the domain inside itself and then smoothing by a smooth convolution operator. | |||
:Suppose ''g'' in H<sup>''k''</sup>('''T'''<sup>2</sup>) annihilates C<sup>∞</sup><sub>''c''</sub>(Ω<sup>''c''</sup>). By compactness, there are finitely many opens ''U''<sub>0</sub>, ''U''<sub>1</sub>, ... , ''U''<sub>''N''</sub> covering the closure of Ω such that the closure of ''U''<sub>0</sub> is disjoint from the boundary and each ''U''<sub>''i''</sub> is an open disc about a boundary point ''z''<sub>''i''</sub> such that in ''U''<sub>''i''</sub> small translations in the direction of the normal vector ''n''<sub>''i''</sub> carry the closure of Ω into Ω. Add an open ''U''<sub>''N''+1</sub> with closure in Ω<sup>''c''</sup> to produce a cover of '''T'''<sup>2</sup> and let ψ<sub>''i''</sup> be a [[partition of unity]] subordinate to this cover. If translation by ''n'' is denoted by ''λ''<sub>''n''</sub>, then | |||
::<math>\displaystyle{g_t=\psi_0 \cdot g +\sum_{i=1}^N \psi_n \lambda_{tn_i} g}</math> | |||
:tend to ''g'' as ''t'' decreases to 0 and still lie in the annihilator, indeed they are in the annihilator for a larger domain than Ω<sup>''c''</sup>, the complement of which lies in Ω. Convolving by smooth functions of small support produces smooth approximations in the annihilator of a slightly smaller domain still with complement in Ω. These are necessarily smooth functions of compact support in Ω. | |||
*'''Further vanishing properties on the boundary:''' The characterization in terms of annihilators shows that a C<sup>''k''</sup> function ''f'' on the closure of Ω lies in H<sup>''k''</sup><sub>0</sub>(Ω) if (and only if) it and its derivatives of order less than ''k'' vanish on the boundary.<ref>{{harvnb|Folland|1995|p=226}}</ref> In fact ''f'' can be extended to '''T'''<sup>2</sup> by setting it to be 0 on Ω<sup>''c''</sup>. The extension ''F'' defines as element in H<sup>''k''</sup>('''T'''<sup>2</sup>) using the formula | |||
::<math>\displaystyle{\|h\|_{(k)}^2=\sum_{j=0}^k {k\choose j} \|\partial_x^j\partial_y^{k-j} h\|^2,}</math> | |||
:and satisfies (''F'',''g'') = 0 for ''g'' in C<sup>∞</sup><sub>''c''</sub>(Ω<sup>''c''</sup>). | |||
*'''Duality:''' For ''k'' ≥ 0, define H<sup>−''k''</sup>(Ω) to be the orthogonal complement in H<sup>−''k''</sup>('''T'''<sup>2</sup>) of H<sup>−''k''</sup><sub>0</sub>(Ω<sup>''c''</sup>). Let ''P''<sub>''k''</sub> be the orthogonal projection onto H<sup>−''k''</sup>(Ω), so that ''Q''<sub>''k''</sub> = ''I'' - ''P''<sub>''k''</sub> is the orthogonal projection onto H<sup>−''k''</sup><sub>0</sub>(Ω<sup>''c''</sup>). When ''k'' = 0, this just gives H<sup>0</sup>(Ω) = L<sup>2</sup>(Ω). If ''f'' is in H<sup>''k''</sup><sub>0</sub>(Ω) and ''g'' in H<sup>−''k''</sup>('''T'''<sup>2</sup>), then | |||
::<math>\displaystyle{(f,g)=(f,P_kg).}</math> | |||
:This implies that under the pairing between H<sup>''k''</sup>('''T'''<sup>2</sup>) and H<sup>−''k''</sup>('''T'''<sup>2</sup>), H<sup>''k''</sup><sub>0</sub>(Ω) and H<sup>−''k''</sup>(Ω) are each other's duals. | |||
*'''Approximation by smooth functions:''' The image of C<sup>∞</sup><sub>c</sub>(Ω) is dense in H<sup>−''k''</sup>(Ω) for ''k'' ≤ 0. This is obvious for ''k'' = 0 since the sum C<sup>∞</sup><sub>c</sub>(Ω) + C<sup>∞</sup><sub>c</sub>(Ω<sup>''c''</sup>) is dense in L<sup>2</sup>('''T'''<sup>2</sup>). Density for ''k'' < follows because the image of L<sup>2</sup>('''T'''<sup>2</sup>) is dense in H<sup>−''k''</sup>('''T'''<sup>2</sup>) and ''P''<sub>''k''</sub> annihilates C<sup>∞</sup><sub>c</sub>(Ω<sup>''c''</sup>). | |||
*'''Canonical isometries:''' The operator (I + ∆)<sup>''k''</sup> gives an isometry of H<sup>2''k''</sup><sub>0</sub>(Ω) into H<sup>0</sup>(Ω) and of H<sup>''k''</sup><sub>0</sub>(Ω) onto H<sup>−''k''</sup>(Ω). In fact the first statement follows because it is true on '''T'''<sup>2</sup>. That (I + ∆)<sup>''k''</sup> is an isometry on H<sup>''k''</sup><sub>0</sub>(Ω) follows using the density of C<sup>∞</sup><sub>c</sub>(Ω) in H<sup>−''k''</sup>(Ω): for ''f'', ''g'' smooth of compact support on Ω | |||
::<math>\displaystyle{\|P_k(I+\Delta)^k f\|_{(-k)}=\sup_{\|g\|_{(-k)}=1} |((I+\Delta)^kf,g)_{(-k})| | |||
=\sup_{\|g\|_{(-k)}=1} |(f,g)|=\|f\|_{(k)}.}</math> | |||
:Since the adjoint map between the duals can by identified with this map, it follows that (I + ∆)<sup>''k''</sup> is a unitary map. | |||
==Application to Dirichlet problem== | |||
{{see also|Dirichlet problem}} | |||
*'''Invertibility of ∆:''' The operator ∆ defines an isomorphism between H<sup>1</sup><sub>0</sub>(Ω) and H<sup>−1</sup>(Ω). In fact it is a Fredholm operator of index 0. The kernel of ∆ in H<sup>1</sup>('''T'''<sup>2</sup>) consists of constant functions and none of these except zero vanish on the boundary of Ω. Hence the kernel of H<sup>1</sup><sub>0</sub>(Ω) is (0) and ∆ is invertible. | |||
:In particular the equation ∆ ''f'' = ''g'' has a unique solution in H<sup>1</sup><sub>0</sub>(Ω) for ''g'' in H<sup>−1</sup>(Ω). | |||
*'''Eigenvalue problem:''' Let ''T'' be the operator on L<sup>2</sup>(Ω) defined by | |||
::<math>\displaystyle{T = R_1\Delta^{-1}R_0,}</math> | |||
:where ''R''<sub>0</sub> is the inclusion of L<sup>2</sup>(Ω) in H<sup>−1</sup>(Ω) and ''R''<sub>1</sub> of H<sup>1</sup><sub>0</sub> in L<sup>2</sup>(Ω), both compact operators by Rellich's theorem. The operator ''T'' is compact, self-adjoint and with (''Tf'',''f'') > 0 for all ''f''. By the [[spectral theorem]], there is a complete orthonormal set of eigenfunctions ''f''<sub>''n''</sub> in L<sup>2</sup>(Ω) with | |||
::<math>\displaystyle{Tf_n=\mu_nf_n,\,\,\mu_n >0,\,\,\mu_n\rightarrow 0.}</math> | |||
:Since μ<sub>''n''</sub> > 0, ''f''<sub>''n''</sub> lies in H<sup>1</sup><sub>0</sub>(Ω). Setting λ<sub>''n''</sub> = 1/ μ<sub>''n''</sub>, the ''f''<sub>''n''</sub> are eigenfunctions of the Laplacian: | |||
::<math>\displaystyle{\Delta f_n = \lambda_n f_n,\,\, \lambda_n>0,\,\, \lambda_n\rightarrow \infty.}</math> | |||
==Sobolev spaces without boundary condition== | |||
To determine the regularity properties of the eigenfunctions ''f''<sub>''n''</sub> and solutions of | |||
:<math>\displaystyle{\Delta f =u,\,\, u\in H^{-1}(\Omega),\,\, f\in H^1_0(\Omega),}</math> | |||
enlargements of the Sobolev spaces H<sup>''k''</sup><sub>0</sub>(Ω) have to be considered. Let C<sup>∞</sup>(Ω<sup>−</sup>) be the space of smooth functions on Ω which with their derivatives extend continuously to the closure of Ω. By [[Borel's lemma]], these are precisely the restrictions of smooth functions on '''T'''<sup>2</sup>. The Sobolev space H<sup>''k''</sup>(Ω) is defined to the Hilbert space completion of this space for the norm | |||
:<math>\displaystyle{\|f\|_{(k)}^2 = \sum_{j=0}^k {k\choose j} \|\partial_x^j\partial_y^{k-j}f\|^2.}</math> | |||
This norm agrees with the Sobolev norm on C<sup>∞</sup><sub>''c''</sub>(Ω) so that H<sup>''k''</sup><sub>0</sub>(Ω) can be regarded as a closed subspace of H<sup>''k''</sup>(Ω). Unlike H<sup>''k''</sup><sub>0</sub>(Ω). H<sup>''k''</sup>(Ω) is not naturally a subspace of H<sup>''k''</sup>('''T'''<sup>2</sup>), but the map restricting smooth functions from '''T'''<sup>2</sup> to the closure of Ω is continuous for the Sobolev norm so extends by continuity to a map ρ<sub>''k''</sub> of H<sup>''k''</sup>('''T'''<sup>2</sup>) into H<sup>''k''</sup>(Ω). | |||
*'''Invariance under diffeomorphism:''' Any diffeomorphism between the closures of two smooth domains induces an isomorphism between the Sobolev space. This is a simple consequence of the chain rule for derivatives. | |||
*'''Extension theorem:''' The restriction of ρ<sub>''k''</sub> to the orthogonal complement of its kernel defines an isomorphism onto H<sup>''k''</sup>(Ω). The extension map ''E''<sub>''k''</sub> is defined to be the inverse of this map: it is an isomorphism (not necessarily norm preserving) of H<sup>''k''</sup>(Ω) onto the orthogonal complement of H<sup>''k''</sup><sub>0</sub>(Ω<sup>''c''</sup>) such that ρ<sub>''k''</sub> ∘ E<sub>''k''</sub> = I. On C<sup>∞</sup><sub>''c''</sub>(Ω), it agrees with the natural inclusion map. Bounded extension maps ''E''<sub>''k''</sub> of this kind from H<sup>''k''</sup>(Ω) to H<sup>''k''</sup>('''T'''<sup>2</sup>) were constructed first constructed by Hestenes and Lions. For smooth curves the [[Seeley extension theorem]] provides an extension which is continuous in all the Sobolev norms. A version of the extension which applies in the case where the boundary is just a Lipschitz curve was constructed by [[Alberto Calderón|Calderón]] using [[Singular integral operators of convolution type|singular integral operators]] and generalized by {{harvtxt|Stein|1970}}. | |||
:It is sufficient to construct an extension ''E'' for a neighbourhood of a closed annulus, since a collar around the boundary is diffeomorphic to an annulus I x '''T''' with I a closed interval in '''T'''. Taking a smooth bump function ψ with 0 ≤ ψ ≤ 1, equal to 1 near the boundary and 0 outside the collar, ''E''( ψ''f'') + (1- ψ)''f'' will provide an extension on Ω. On the annulus, the problem reduces to finding an extension for C<sup>''k''</sup>(I) in C<sup>''k''</sup>('''T'''). Using a partition of unity the task of extending reduces to a neighbourhood of the end points of ''I''. Assuming 0 is the left end point, an extension is given locally by | |||
::<math>\displaystyle{E(f) = \sum_{m=0}^k a_m f(-x/(m+1)).}</math> | |||
:Matching the first derivatives of order ''k'' or less at 0, gives | |||
::<math>\displaystyle{\sum_{m=0}^k (-m-1)^{-k} a_m =1.}</math> | |||
:This matrix equation is solvable because the determinant is non-zero by [[Vandermonde determinant|Vandermonde's formula]]. It is straightforward to check that the formula for ''E''(''f''), when appropriately modified with bump functions, leads to an extension which is continuous in the above Sobolev norm.<ref>{{harvnb|Folland|1995}}</ref> | |||
*'''Restriction theorem:''' The restriction map ρ<sub>''k''</sub> is surjective with ker ρ<sub>''k''</sub> = H<sup>''k''</sup><sub>0</sub>(Ω<sup>''c''</sup>). This is an immediate consequence of the extension theorem and the support properties for Sobolev spaces with boundary condition. | |||
*'''Duality:''' H<sup>''k''</sup>(Ω) is naturally the dual of H<sup>−''k''</sup><sub>0</sub>(Ω). Again this is an immediate consequence of the restriction theorem. Thus the Sobolev spaces form a chain: | |||
::<math>\displaystyle{\cdots\subset H^{2}(\Omega) \subset H^{1}(\Omega) \subset H^0(\Omega) \subset H^{-1}_0(\Omega) \subset H^{-2}_0(\Omega) \subset \cdots}</math> | |||
:The differentiation operators ∂<sub>''x''</sub>, ∂<sub>''y''</sub> carry each Sobolev space into the larger one with index 1 less. | |||
*'''Sobolev embedding theorem:''' H<sup>''k''+2</sup>(Ω) is contained in C<sup>''k''</sup>(Ω<sup>−</sup>). This is an immediate consequence of the extension theorem and the Sobolev embedding theorem for H<sup>''k''+2</sup>('''T'''<sup>2</sup>). | |||
*'''Characterization:''' H<sup>''k''</sup>(Ω) consists of ''f'' in L<sup>2</sup>(Ω) = H<sup>0</sup>(Ω) such that all the derivatives ∂<sup>α</sup>''f'' lie in L<sup>2</sup>(Ω) for |α| ≤ ''k''.Here the derivatives are taken within the chain of Sobolev spaces above.<ref>See: | |||
*{{harvnb|Agmon|2010}} | |||
*{{harvnb|Folland|1995|pp=219–223}} | |||
*{{harvnb|Chazarain|Piriou|1982|p=94}}</ref> Since C<sup>∞</sup><sub>''c''</sub>(Ω) is weakly dense in H<sup>''k''</sup>(Ω), this condition is equivalent to the existence of L<sup>2</sup> functions ''f''<sub>α</sub> such that | |||
::<math>\displaystyle{(f_\alpha,\varphi)=(-1)^{|\alpha|} (f,\partial^\alpha \varphi)}</math> | |||
:for |α| ≤ ''k'' and φ in C<sup>∞</sup><sub>''c</sub>(Ω). | |||
:To prove the characterization, note that if ''f'' is in H<sup>''k''</sup>(Ω), then ∂<sup>α</sup>''f'' lies in H<sup>''k''−|α|</sup>(Ω) and hence in H<sup>0</sup>(Ω) = L<sup>2</sup>(Ω). Conversely the result is well-known for the Sobolev spaces H<sup>''k''</sup>('''T'''<sup>2</sup>): the assumption implies that the (∂<sub>''x''</sub> -i∂<sub>''y''</sub>)<sup>''k''</sup> ''f'' is in L<sup>2</sup>('''T'''<sup>2</sup>) and the corresponding condition on the Fourier coefficients of ''f'' shows that ''f'' lies in H<sup>''k''</sup>('''T'''<sup>2</sup>). Similarly the result an be proved directly for an annulus [−δ,δ] x '''T'''. In fact by the argument on '''T'''<sub>2</sub> the restriction of ''f'' to any smaller annulus [−δ',δ'] x '''T''' lies in H<sup>''k''</sub>: equivalently the restriction of the function ''f''<sub>''R''</sub>(''x'',''y'') = ''f''(''Rx'',''y'') lies in H<sup>''k''</sup> for ''R'' > 1. On the other hand ∂<sup>α</sup>''f''<sub>''R''</sub> tends to ∂<sup>α</sup>''f'' in L<sup>2</sup> as ''R'' tends to 1, so that ''f'' must lie in H<sup>''k''</sup>. The case for a general domain Ω reduces to these two cases since ''f'' can be written as ''f'' = ψ''f'' + (1 − ψ)''f'' with ψ a bump function supported in Ω such that 1 − ψ is supported in a collar of the boundary. | |||
*'''Regularity theorem:''' If ''f'' in L<sup>2</sup>(Ω) has both derivatives ∂<sub>''x''</sub>''f'' and ∂<sub>''y''</sub>''f'' in H<sup>''k''</sup>(Ω) then ''f'' lies in H<sup>''k''+1</sup>(Ω). This is an immediate consequence of the characterization of H<sup>''k''</sup>(Ω) above. In fact if this is true even when satisfied at the level of distributions: if there are functions ''g'', ''h'' in H<sup>''k''</sup>(Ω) such that (''g'',φ) = (''f'',φ<sub>''x''</sub>) and (''h'',φ) = (''f'',φ<sub>''y''</sub>) for φ in C<sup>∞</sup><sub>''c''</sub>(Ω), then ''f'' is in H<sup>''k''+1</sup>(Ω). | |||
*'''Rotations on an annulus:''' For an annulus ''I'' x '''T''', the extension map to '''T'''<sup>2</sup> is by construction equivariant with respect to rotations in the second variable, | |||
::<math>\displaystyle{R_t f(x,y)=f(x,y+t).}</math> | |||
:On '''T'''<sup>2</sup> it is known that if ''f'' is in H<sup>''k''</sup>, then the ''difference quotient'' δ<sub>''h''</sub>''f'' = ''h''<sup>−1</sup>(''R''<sub>''h''</sub>''f'' - ''f'') tends to ∂<sub>''y''</sub> ''f'' in H<sup>''k''−1</sup>; if the difference quotients are bounded in ''H''<sup>''k''</sup> then ∂<sub>''y''</sub> ''f'' lies in H<sup>''k''</sup>. Both assertions are consequences of the formula: | |||
::<math>\displaystyle{\widehat{\delta_h f}(m,n) = h^{-1}(e^{-ihn}-1)\widehat{f}(m,n)=-\int_0^1 in e^{-inht}\, dt \,\,\widehat{f}(m,n).}</math> | |||
:These results on '''T'''<sup>2</sup> imply analogous results on the annulus using the extension. | |||
==Regularity for Dirichlet problem== | |||
*'''Regularity for dual Dirichlet problem:''' If ∆''u'' = ''f'' with ''u'' in H<sup>1</sup><sub>0</sub>(Ω) and ''f'' in H<sup>''k''−1</sup>(Ω) with ''k'' ≥ 0, then ''u'' lies in H<sup>''k''+1</sup>(Ω). | |||
:Take a decomposition ''u'' = ψ''u'' + (1 − ψ)''u'' with ψ supported in Ω and 1 − ψ supported in a collar of the boundary. Standard Sobolev theory for '''T'''<sup>2</sub> can be applied to ψ''u'': elliptic regularity implies that it lies in H<sup>''k''+1</sup>('''T'''<sup>2</sup>) and hence H<sup>''k''+1</sup>(Ω). ''v'' = (1 − ψ)''u'' lies in H<sup>1</sup><sub>0</sub> of a collar, diffeomorphic to an annulus, so it suffices to prove the result with Ω a collar and ∆ replaced by | |||
::<math>\displaystyle{\Delta_1=\Delta -[\Delta,\psi]=\Delta + (p\partial_x + q\partial_y - \Delta \psi)=\Delta +X.}</math> | |||
:The proof<ref>{{harvnb|Taylor|2011}}</ref> proceeds by induction on ''k'', proving simultaneously the inequality | |||
::<math>\displaystyle{\|u\|_{(k+1)} \le C\|\Delta_1 u\|_{(k-1)} + C \|u\|_{(k)},}</math> | |||
:for some constant ''C'' depending only on ''k''. It is straightforward to establish this inequality for ''k'' = 0, where by density ''u'' can be taken to be smooth of compact support in Ω: | |||
::<math>\displaystyle{\|u\|_{(1)}^2 =|(\Delta u, u)|\le |(\Delta_1 u,u)| +|(Xu,u)| \le \|\Delta_1 u\|_{(-1)}\|u\|_{(1)} +C^\prime \|u\|_{(1)}\|u\|_{(0)}.}</math> | |||
:The collar is diffeomorphic to an annulus. The rotational flow ''R''<sub>''t''</sub> on the annulus induces a flow ''S''<sub>''t''</sub> on the collar with corresponding vector field ''Y'' = ''r'' ∂<sub>''x''</sub> + ''s'' ∂<sub>''y''</sub>. Thus ''Y'' corresponds to the vector field ∂<sub>θ</sub>. The radial vector field on the annulus ''r''∂<sub>''r''</sub> is a commuting vector field which on the collar gives a vector field ''Z'' = ''p'' ∂<sub>''x''</sub> + ''q'' ∂<sub>''y''</sub> proportional to the normal vector field. The vector fields ''Y'' and ''Z'' commute. | |||
:The difference quotients δ<sub>''h''</sub> ''u'' can be formed for the flow ''S''<sub>''t''</sub>. The commutators [δ<sub>''h''</sub>,∆<sub>1</sub>] are second order differential operators from H<sup>''k''+1</sup>(Ω) to H<sup>''k''−1</sup>(Ω). Their operators norms are uniformly bounded for ''h'' near 0; for the computation can be carried out on the annulus where the commutator just replaces the coefficients of ∆<sub>1</sub> by their difference quotients composed with ''S''<sub>''h''</sub>. On the other hand ''v'' = δ<sub>''h''</sub> ''u'' lies in H<sup>1</sup><sub>0</sub>(Ω), so the inequalities for ''u'' apply equally well for ''v'': | |||
::<math>\displaystyle{\|\delta_h u\|_{(k+1)} \le C\|\Delta_1 \delta_h u\|_{(k-1)} + C \|\delta_h u\|_{(k)} | |||
\le C \|\delta_h \Delta_1 u\|_{(k-1)} + C\|[\delta_h,\Delta_1] u\|_{(k-1)} + C \|\delta_h u\|_{(k)} \le C\|\Delta_1 u\|_{(k)} + C^\prime \|u\|_{(k+1)}.}</math> | |||
:The uniform boundedness of the difference quotients δ<sub>''h''</sub> ''u'' implies that ''Y'' ''u'' lies in H<sup>''k''+1</sup>(Ω) with | |||
::<math>\displaystyle{\|Y u\|_{(k+1)} \le C\|\Delta_1 u\|_{(k)} + C^\prime \|u\|_{(k+1)}.}</math> | |||
:It follows that ''V'' ''u'' lies in H<sup>''k''+1</sup>(Ω) where ''V'' is the vector field | |||
::<math>\displaystyle{V =(r^2+s^2)^{-1/2}Y = a\partial_x + b\partial_y,}</math> | |||
:where ''a''<sup>2</sup> + ''b''<sup>2</sup> = 1. Moreover ''Vu'' satisfies a similar inequality to ''Yu''. | |||
::<math>\displaystyle{\|V u\|_{(k+1)} \le C^{\prime\prime}(\|\Delta_1 u\|_{(k)} + \|u\|_{(k+1)}).}</math> | |||
:Let ''W'' be the orthogonal vector field | |||
::<math>\displaystyle{W=-b\partial_x + a\partial_y.}</math> | |||
:It can also be written as ξ''Z'' for some smooth nowhere vanishing function ξ on a neighbourhood of the collar. | |||
:It suffices to show that ''Wu'' lies in H<sup>''k''+1</sup>(Ω). For then | |||
::<math>\displaystyle{(V \pm iW)u =(a\mp i b)(\partial_x \pm i \partial_y)u,}</math> | |||
:so that ∂<sub>''x''</sub>''u'' and ∂<sub>''y''</sub>''u'' lie in H<sup>''k''+1</sup>(Ω) and ''u'' must lie in H<sup>''k''+2</sup>(Ω). | |||
:To check the result on ''Wu'', it is enough to show that ''VWu'' and ''W''<sup>2</sup>''u'' lie in H<sup>''k''</sup>(Ω). Note that | |||
::<math>\displaystyle{A=\Delta - V^2 - W^2,\,\,\, B=[V,W],}</math> | |||
:are vector fields. But then | |||
::<math>\displaystyle{W^2u=\Delta u - V^2u - Au,\,\,\, VWu =WVu + Bu,}</math> | |||
:with all terms on the right hand side in H<sup>''k''</sup>(Ω). Moreover the inequalities for ''Vu'' show that | |||
::<math>\|Wu\|_{(k+1)} \le C(\|VWu\|_{(k)} + \|W^2u\|_{(k)}) | |||
\le C\|(\Delta - V^2 -A)u\|_{(k)} + C \|(WV+B)u\|_{(k)} \le C_1 \|\Delta_1 u\|_{(k)} + C_1 \|u\|_{(k+1)}.</math> | |||
:Hence | |||
::<math>\displaystyle{\|u\|_{(k+2)} \le C(\|Vu\|_{(k+1)} + \|Wu\|_{(k+1)}) | |||
\le C^\prime \|\Delta_1 u\|_{(k)} + C^\prime \|u\|_{(k+1)}.}</math> | |||
*'''Smoothness of eigenfunctions.''' It follows by induction from the regularity theorem for the dual Dirichlet problem that the eigenfunctions of ∆ in H<sup>1</sup><sub>0</sub>(Ω) lie in C<sup>∞</sup>{Ω<sup>−</sup>). Moreover any solution of ∆''u'' = ''f'' with ''f'' in C<sup>∞</sup>{Ω<sup>-</sup>) and ''u'' in H<sup>1</sup><sub>0</sub>(Ω) must have ''u'' in C<sup>∞</sup>{Ω<sup>-</sup>). In both cases by the vanishing properties, the eigenfunctions and ''u'' vanish on the boundary of Ω. | |||
*'''Solving the Dirichlet problem.''' The dual Dirichlet problem can be used to solve the Dirichlet problem: | |||
::<math>\displaystyle{\Delta f|_\Omega = 0,\,\, f|_{\partial\Omega} =g,}</math> | |||
:with ''g'' a smooth function on ∂Ω. By Borel's lemma ''g'' is the restriction of a function ''G'' in C<sup>∞</sup>(Ω<sup>−</sup>). Let ''F'' be the smooth solution of ∆''F'' = ∆''G'' with ''F'' = 0 on ∂Ω. Then ''f'' = ''G'' − ''F'' solves the Dirichlet problem. By the [[maximal principle]], the solution is unique.<ref>{{harvnb|Folland|1995|p=84}}</ref> | |||
==Application to smooth Riemann mapping theorem== | |||
The solution to the Dirichlet problem can be used to prove a strong form of the [[Riemann mapping theorem]] for simply connected domains with smooth boundary. The method also applies to a region diffeomorphic to an annulus.<ref>{{harvnb|Taylor|2011|pp=323–325}}</ref> For multiply connected regions with smooth boundary {{harvtxt|Schiffer|Hawley|1962}} have given a method for mapping the region onto a disc with circular holes. Their method involves solving the Dirichlet problem with a non-linear boundary condition. They construct a function ''g'' harmonic in the interior of Ω with | |||
:<math>\displaystyle{\partial_n g = \kappa - K e^g}</math> | |||
on ∂Ω, where κ is the curvature of the boundary curve, ∂<sub>''n''</sub> is the derivative in the direction of the normal to ∂Ω and ''K'' is constant on each boundary component. | |||
{{harvtxt|Taylor|2011}} gives a proof of the Riemann mapping theorem for a simply connected domain Ω with smooth boundary. Translating if necessary, it can be assumed that 0 lies in Ω. The solution of the Dirichlet problem shows that there is a unique smooth function ''U''(''z'') on the closure of Ω which is harmonic in Ω and equal to −log |''z''| on the boundary. Define the [[Green's function]] by ''G''(''z'') = log |''z''| + ''U''(''z''). It vanishes on the boundary and is harmonic on Ω away from 0. | |||
The [[harmonic conjugate]] ''V'' of ''U'' is the unique real function on Ω such that ''U'' + ''i'' ''V'' is holomorphic. As such it must satisfy the [[Cauchy-Riemann equations]]: | |||
:<math>\displaystyle{U_x=-V_y,\,\, U_y=V_x.}</math> | |||
The solution is given by | |||
:<math>\displaystyle{V(z)=\int_0^z -U_y dx + V_x dy,}</math> | |||
where the integral is taken over any path in the closure of Ω. It is easily verified that ''V''<sub>''x''</sub> and ''V''<sub>''y''</sub> are exist and are given by the corresponding derivatives of ''U''. Thus ''V'' is a smooth function on the closure of Ω, vanishing at 0. By the Cauchy-Riemann ''f'' = ''U'' + ''i'' ''V'' is smooth on the closure of Ω, holomorphic on | |||
Ω and ''f''(0) = 0. The function ''H'' = arg ''z'' + ''V''(''z'') is only defined up to multiples of 2π, but the function | |||
:<math>\displaystyle{F(z) =e^{G(z)+iH(z)}= z e^{f(z)}}</math> | |||
is a holomorphic on Ω and smooth on its closure. By construction it satisfies ''F''(0) = 0 and |''F''(''z'')| = 1 for ''z'' on the boundary of Ω. Since ''z'' has [[winding number]] 1, so too does ''F''(''z''). On the other hand ''F''(''z'') = 0 only for ''z'' =0 where there is a simple zero. So by the [[argument principle]] ''F'' assumes every value in the unit disc exactly once and ''F'' ' does not vanish inside Ω. To check that the derivative on the boundary curve is non-zero amounts to computing the derivative of ''e''<sup>''iH''</sup>, i.e. the derivative of ''H'' should not vanish on the boundary curve. By the Cauchy-Riemann equations these tangential derivative are up to a sign the [[directional derivative]] in the direction of the normal to the boundary. But ''G'' vanishes on the boundary and is strictly negative in Ω since |''F''| = ''e''<sup>''G''</sup>. The [[Hopf lemma]] implies that the directional derivative of ''G'' in the direction of the outward normal is strictly positive. So on the boundary curve ''F'' has nowhere vanishing derivative. Since the boundary curve has winding number one, ''F'' defines a diffeomorphism of the boundary curve onto the unit circle. Accordingly ''F'' is a smooth diffeomorphism of the closure of Ω onto the closed unit disk, which restricts to a holomorphic map of Ω onto the open unit disk and a smooth diffeomorphism between the boundaries. | |||
Similar arguments can be applied to prove the Riemann mapping theorem for a doubly connected domain Ω bounded by simple smooth curves | |||
''C''<sub>''i''</sub> (the inner curve) and ''C''<sub>''o''</sub> (the outer curve). B tranlsating we can assume 1 lies on the outer boundary. Let ''u'' be the smooth solution of the Dirichlet problem with ''U'' = 0 on the outer curve and −1 on the inner curve. By the [[maximum principle]] 0 < ''u''(''z'') < 1 for ''z'' in Ω and so by the [[Hopf lemma]] the normal derivatives of ''u'' are negative on the outer curve and positive on the inner curve. The integral of −''u''<sub>''y''</sub> ''dx'' + ''u''<sub>''y''</sub> ''dx'' over the boundary is zero by Stoke's theorem so the contributions from the boundary curves cancel. On the other hand on each boundary curve the contribution is the integral of the normal derivative along the boundary. So there is a constant ''c'' > 0 such that ''U'' = ''cu'' satisfies | |||
:<math>\displaystyle{\int_{C} -U_y \,dx + U_x \, dy = 2\pi}</math> | |||
on each boundary curve. The harmonic conjugate ''V'' of ''U'' can again be defined by | |||
:<math>\displaystyle{V(z)=\int_1^z -u_y \,dx + u_x \, dy}</math> | |||
and is well-defined up to multiples of 2π. The function | |||
:<math>\displaystyle{F(z)=e^{U(z) + i V(z)}}</math> | |||
is smooth on the closure of Ω and holomorphic in Ω. On the outer curve |''F''| = 1 and on the inner curve |''F''| = ''e''<sup>−''c''</sup> = ''r'' < 1. The tangential derivatives on the outer curves are nowhere vanishing by the Cauchy-Riemann equations, since the normal derivatives are nowhere vanishing. The normalization of the integrals implies that ''F'' restricts to a diffeonmorphism between the boundary curves and the two concentric circles. Since the images of outer and inner curve have winding number 1 and 0 about any point in the annulus, an application of the argument principle implies that ''F'' assumes every value within the annulus ''r'' < |''z''| < 1 exactly once; since that includes mutliplicities, the complex derivative of ''F'' is nowhere vanishing in Ω. This ''F'' is a smooth diffeomorphism of the closure of Ω onto the closed annulus ''r'' ≤ |''z''| ≤ 1, restricting to a holomorphic map in the interior and a smooth diffeomorphism on both boundary curves. | |||
==Trace map== | |||
The restriction map τ of C<sup>∞</sup>('''T'''<sup>2</sup>) onto C<sup>∞</sup>('''T''') = C<sup>∞</sup>(1 × '''T''') extends to a continuous map H<sup>''k''</sup>('''T'''<sup>2</sup>) into H<sup>''k'' − ½</sup>('''T''') for ''k'' ≥ 1.<ref>{{harvnb|Chazarain|Piriou|1982}}</ref> In fact | |||
:<math>\displaystyle{\widehat{\tau f}(n)=\sum_m \widehat{f}(m,n),}</math> | |||
so the [[Cauchy–Schwarz inequality]] yields | |||
:<math>|\widehat{\tau f}(n)|^2 (1+n^2)^{k-1/2}\le \left(\sum_m {(1+n^2)^{k-1/2}\over (1+m^2+n^2)^{k}}\right)\cdot\left(\sum_m |\widehat{f}(m,n)|^2 (1+m^2+n^2)^k\right) \le C_k \sum_m|\widehat{f}(m,n)|^2 (1+m^2+n^2)^k,</math> | |||
where, by the [[integral test]], | |||
:<math>\displaystyle{C_k=\sup_n \sum_m {(1+n^2)^{k-1/2}\over (1+m^2 +n^2)^k} <\infty,\,\,\, c_k=\inf_n \sum_m {(1+n^2)^{k-1/2}\over (1+m^2 +n^2)^k}>0.}</math> | |||
The map τ is onto since a continuous extension map ''E'' can be constructed from H<sup>''k'' − ½</sup>('''T''') to H<sup>''k''</sup>('''T'''<sup>2</sup>).<ref>{{harvnb|Taylor|2011|p=275}}</ref><ref>{{harvnb|Renardy|Rogers|2004|214-218}}</ref> In fact set | |||
:<math>\displaystyle{\widehat{Eg}(m,n)=\lambda_{n}^{-1} \widehat{g}(n)\cdot {(1+n^2)^{k-1/2}\over (1+n^2+m^2)^k},}</math> | |||
where | |||
:<math>\displaystyle{\lambda_n=(1+n^2)^{k-1/2}\sum_m (1+m^2+n^2)^{-k} < C_k.}</math> | |||
Thus λ<sub>''n''</sub> > c<sub>''k''</sub>. If ''g'' is smooth, then by construction ''Eg'' restricts to ''g'' on 1 × '''T'''. Moreover ''E'' is a bounded linear map since | |||
:<math>\|Eg\|_{(k)}^2=\sum_{m,n}|\widehat{Eg}(m,n)|^2 (1+m^2+n^2)\le c_k^{-2}\sum_{m,n} |\widehat{g}(n)|^2 (1+n^2)^{2k-1} (1+m^2+n^2)^{-k} \le c_k^{-2}C_k \|g\|_{k-1/2}^2.</math> | |||
It follows that there is a trace map τ of H<sup>''k''</sup>(Ω) onto H<sup>''k'' − ½</sup>(∂Ω). Indeed take a tubular neighbourhood of the boundary and a smooth function ψ supported in the collar and equal to 1 near the boundary. Multiplication by ψ carries functions into H<sup>''k''</sup> of the collar, which can be identified with H<sup>''k''</sup> of an annulus for which there is a trace map. The invariance under diffeomorphims (or coordinate change) of the half-integer Sobolev spaces on the circle follows from the fact that an equivalent norm on ''H''<sup>''k'' + ½</sup>('''T''') is given by<ref>{{harvnb|Hörmander|1990|pp=240–241}}</ref> | |||
:<math>\|f\|_{[k+1/2]}^2 = \|f\|_{(k)}^2 + \int_0^{2\pi}\int_0^{2\pi} {|f^{(k)}(s)-f^{(k)}(t)|^2\over|e^{is} -e^{it}|^{2}}\,ds\, dt.</math> | |||
It is also a consequence of the properties of τ and ''E'' (the "trace theorem").<ref>{{harvnb|Renardy|Rogers|2004}}</ref> In fact any diffeomorphism ''f'' of '''T''' induces a diffeomorphism ''F'' of '''T'''<sup>2</sup> by acting only on the second factor. Invariance of H<sup>''k''</sup>('''T'''<sup>2</sup>) under the induced map ''F''* therefore implies invariance of H<sup>''k'' − ½</sup>('''T''') under ''f''*, since ''f''* = τ ∘ ''F''* ∘ ''E''. | |||
Further consequences of the trace theorem are the two exact sequences<ref>{{harvnb|Chazarain|Piriou|1982}}</ref><ref>{{harvnb|Renardy|Rogers|2004}}</ref> | |||
:<math>\displaystyle{(0)\rightarrow H^1_0(\Omega) \rightarrow H^1(\Omega) \rightarrow H^{1/2}(\partial\Omega) \rightarrow (0)}</math> | |||
and | |||
:<math>\displaystyle{(0)\rightarrow H^2_0(\Omega) \rightarrow H^2(\Omega) \rightarrow H^{3/2}(\partial\Omega) \oplus H^{1/2}(\partial\Omega) \rightarrow (0),}</math> | |||
where the last map takes ''f'' in H<sup>2</sup>(Ω) to ''f''|<sub>∂Ω</sub> and ∂<sub>''n''</sub>''f''|<sub>∂Ω</sub>. There are generalizations of these sequences to H<sup>''k''</sup>(Ω) involving higher powers of the normal derivative in the trace map: | |||
:<math>\displaystyle{(0)\rightarrow H^k_0(\Omega) \rightarrow H^k(\Omega) \rightarrow \bigoplus_{j=1}^k H^{j-/2}(\partial\Omega) \rightarrow (0).}</math> | |||
The trace map to H<sup>''j'' − ½</sup>(∂Ω) takes ''f'' to ∂<sub>''n''</sub><sup>''k'' − ''j''</sup>''f''|<sub>∂Ω</sub> | |||
==Abstract formulation of boundary value problems== | |||
The Sobolev space approach to the Neumann problem cannot be phrased quite as directly as that for the Dirichlet problem. The main reason is that for a function ''f'' in H<sup>1</sup>(Ω), the normal derivative ∂<sub>''n''</sub>''f''|<sub>∂Ω</sub> cannot be a priori defined at the level of Sobolev spaces. Instead an alternative formulation of boundary value problems for the Laplacian Δ on a bounded region Ω in the plane is used. It employs '''[[Dirichlet form]]s''', sesqulinear bilinear forms on H<sup>1</sup>(Ω), H<sup>1</sup><sub>0</sub> or an intermediate closed subspace. Integration over the boundary is not involved in defining the Dirichlet form. Instead, if the Dirichlet form satisfies a certain positivity condition, termed '''coerciveness''', solution can be shown to exist in a weak sense, so-called "weak solutions". A general regularity theorem than implies that the solutions of the boundary value problem must lie in H<sup>2</sup>(Ω), so that they are strong solutions and satisfy boundary conditions involving the restriction of a function and its normal derivative to the boundary. The Dirichlet problem can equally well be phrased in these terms, but because the trace map ''f''|<sub>∂Ω</sub> is already defined on H<sup>1</sup>(Ω), Dirichlet forms do not need to be mentioned explicitly and the operator formulation is more direct. A unified discussion is given in {{harvtxt|Folland|1995}} and briefly summarised below. It is explained how the Dirichlet problem, as discussed above, fits into this framework. Then a detailed treatment of the Neumann problem from this point of view is given following {{harvtxt|Taylor|2011}}. | |||
The HIlbert space formulation of boundary value problems for the Laplacian Δ on a bounded region Ω in the plane proceeds from the following data:<ref>{{harvnb|Folland|1995|pp=231–248}}</ref> | |||
*A closed subspace ''H'' lying between H<sup>1</sup><sub>0</sub>(Ω) and H<sup>1</sup>(Ω) | |||
*A Dirichlet form for Δ given by a bounded Hermitian bilinear form ''D''(''f'',''g'') defined for ''f'', ''g'' in H<sup>1</sup>(Ω) such that ''D''(''f'',''g'')=(∆ ''f'',''g'') for ''f'', ''g'' in H<sup>1</sup><sub>0</sub>(Ω). | |||
*''D'' is coercive, i.e. there is a positive constant ''C'' and a non-negative constant λ such that ''D''(''f'',''f'') ≥ ''C'' (''f'',''f'')<sub>(1)</sub> − λ(''f'',''f''). | |||
A '''weak solution''' of the boundary value problem given initial data ''f'' in L<sup>2</sup>(Ω) is a function ''u'' in ''H'' such that | |||
:<math>\displaystyle{D(f,g)=(u,g)}</math> | |||
for all ''g'' in ''H''. | |||
For both the Dirichlet and Neumann problem | |||
:<math>\displaystyle{D(f,g)=(f_x,g_x) + (f_y,g_y).}</math> | |||
For the Dirichlet problem ''H'' = H<sup>1</sup><sub>0</sub>(Ω). In this case | |||
:<math>\displaystyle{D(f,g)=(\Delta f,g)}</math> | |||
for ''f'', ''g'' in ''H''. By the trace theorem the solution satisfies ''u''|<sub>Ω</sub> = 0 in H<sup>½</sup>(∂Ω). | |||
For the Neumann problem ''H'' is taken to be H<sup>1</sup>(Ω). | |||
==Application to Neumann problem== | |||
The classical Neumann problem on Ω consists in solving the boundary value problem | |||
:<math>\displaystyle{\Delta u =f}</math> | |||
with ''f'' in C<sup>∞</sup>(Ω<sup>−</sup>) and ''u'' in C<sup>∞</sup>(Ω<sup>−</sup>) and satisfying the Neumann boundary condition | |||
:<math>\displaystyle{\partial_n u =0.}</math> | |||
[[Green's theorem]] implies that for ''u'', ''v'' in C<sup>∞</sup>(Ω<sup>−</sup>) | |||
:<math>\displaystyle{(\Delta u,v)= (u_x,v_x) + (u_y,v_y) - (\partial_n u,v)_{\partial \Omega}.}</math> | |||
Thus if Δ''u'' = 0 in Ω and satisfies the Neumann boundary conditions, ''u''<sub>''x''</sub>, ''u''<sub>''y''</sub> = 0, and so | |||
''u'' is constant in Ω. | |||
Hence the Neumann problem has a unique solution up to adding constants.<ref>{{harvnb|Taylor|2011}}</ref> | |||
Consider the Hermitian form on H<sup>1</sup>(Ω) defined by | |||
:<math>\displaystyle{D(f,g)=(u_x,v_x) + (u_y,v_y).}</math> | |||
Since H<sup>1</sup>(Ω) is in duality with H<sup>−1</sup><sub>0</sub>(Ω), there is a unique element ''Lu'' in H<sup>−1</sup><sub>0</sub>(Ω) such that | |||
:<math>\displaystyle{D(u,v) =(Lu,v).}</math> | |||
The map ''I'' + ''L'' is an isometry of H<sup>1</sup>(Ω) onto H<sup>−1</sup><sub>0</sub>(Ω), so in particular ''L'' is bounded. | |||
In fact | |||
:<math>\displaystyle{((L+I)u,v)=(u,v)_{(1)}.}</math> | |||
So | |||
:<math>\|(L+I)u\|_{(-1)} =\sup_{\|v\|_{(1)}=1} |((L+I)u,v)|= \sup_{\|v\|_{(1)}=1} |(u,v)_{(1)}|=\|u\|_{(1)}.</math> | |||
On the other hand any ''f'' in H<sup>−1</sup><sub>0</sub>(Ω) defines a bounded conjugate-linear form on H<sup>1</sup>(Ω) sending ''v'' to (''f'',''v''). By the [[Riesz–Fischer theorem]], there exists ''u'' in H<sup>1</sup>(Ω) such that | |||
:<math>\displaystyle{(f,v)=(u,v)_{(1)}.}</math> | |||
Hence (''L'' + ''I'')''u'' = ''f'' and so ''L'' + ''I'' is surjective. Define a bounded linear operator ''T'' on L<sup>2</sup>(Ω) by | |||
:<math>\displaystyle{T=R_1(I+L)^{-1} R_0,}</math> | |||
where ''R''<sub>1</sub> is the map H<sup>1</sup>(Ω) → L<sup>2</sup>(Ω), a compact operator, and ''R''<sub>0</sub> is the map | |||
L<sup>2</sup>(Ω) → H<sup>−1</sup><sub>0</sub>(Ω), its adjoint, so also compact. | |||
The operator ''T'' has the following properties: | |||
*''T'' is a contraction since it is a composition of contractions | |||
*''T'' is compact, since ''R''<sub>0</sub> and ''R''<sub>1</sub> are compact by Rellich's theorem | |||
*''T'' is self-adjoint, since if ''f'' and ''g'' are in L<sup>2</sup>(Ω), they can be written ''f'' =(''L'' + ''I'')''u'', ''g'' = (''L'' + ''I'')''v'' with ''u'', ''v'' in H<sup>1</sup>(Ω) so | |||
::<math>\displaystyle{(Tf,g)=(u,(I+L)v)=(u,v)_{(1)}=((I+L)u,v)= (f,Tg).}</math> | |||
*''T'' has positive spectrum and kernel (0), for | |||
::<math>\displaystyle{(Tf,f)=(u,u)_{(1)}\ge 0,}</math> | |||
:and ''Tf'' = 0 implies ''u'' = 0 and hence ''f'' = 0. | |||
*There is a complete orthonormal basis ''f''<sub>''n''</sub> of L<sup>2</sup>(Ω) consisting of eigenfunctions of ''T''. Thus | |||
::<math>\displaystyle{Tf_n=\mu_nf_n}</math> | |||
:with 0 < μ<sub>''n''</sub> ≤ 1 and μ<sub>''n''</sub> decreasing to 0. | |||
*The eigenfunctions all lie in H<sup>1</sup>(Ω) since the image of ''T'' lies in H<sup>1</sup>(Ω). | |||
*The ''f''<sub>''n''</sub> are eigenfunctions of ''L'' with | |||
::<math>\displaystyle{Lf_n=\lambda_nf_n,\,\,\,\,\, \lambda_n=\mu_n^{-1} -1.}</math> | |||
:Thus λ<sub>''n''</sub> are non-negative and increase to ∞. | |||
*The eigenvalue 0 occurs with multiplicity one and corresponds to the constant function. For if ''u'' in H<sup>1</sup>(Ω) satisfies ''Lu'' = 0, then | |||
::<math>\displaystyle{(u_x,u_x) + (u_y,u_y)=(Lu,u)=0,}</math> | |||
:so ''u'' is constant. | |||
==Regularity for Neumann problem== | |||
===Weak solutions are strong solutions=== | |||
The first main regularity result shows that a weak solution expressed in terms of the operator ''L'' and the Dirichlet form | |||
''D'' is a strong solution in the classical sense, expressed in terms of the Laplacian Δ and the Neumann boundary conditions. Thus if ''u'' = ''Tf'' with ''u'' in H<sup>1</sup>(Ω) and ''f'' in L<sup>2</sup>(Ω), then ''u'' in fact lies in H<sup>2</sup>(Ω), satisfies Δ''u'' + ''u'' = ''f'' and ∂<sub>''n''</sub>''u''|<sub>∂Ω</sub> = 0. Moreover for some constant ''C'' independent of ''u'', | |||
:<math>\displaystyle{\|u\|_{(2)} \le C\|\Delta u\|_{(0)} + C \|u\|_{(1)}.}</math> | |||
Note that | |||
:<math>\displaystyle{\|u\|_{(1)} \le \|L u\|_{(-1)} + \|u\|_{(0)},}</math> | |||
since | |||
:<math>\displaystyle{\|u\|_{(1)}^2 =|(L u, u)| +\|u\|^2_{(0)}\le \|L u\|_{(-1)}\|u\|_{(1)} + \|u\|_{(0)}\|u\|_{(1)}.}</math> | |||
Take a decomposition ''u'' = ψ''u'' + (1 − ψ)''u'' with ψ supported in Ω and 1 − ψ supported in a collar of the boundary. | |||
The operator ''L'' is characterized by | |||
:<math>\displaystyle{(Lf,g)=(f_x,g_x)+(f_y,g_y)= (\Delta f,g)_\Omega - (\partial_n f,g)_{\partial\Omega}}</math> | |||
for ''f'', ''g'' in C<sup>∞</sup>(Ω<sup>−</sup>). Then | |||
:<math>\displaystyle{([L,\psi]f,g)=([\Delta,\psi]f,g),}</math> | |||
so that | |||
:<math>\displaystyle{[L,\psi]=-[L,1-\psi]=\Delta\psi +2\psi_x\partial_x + 2\psi_y\partial_y.}</math> | |||
The function ''v'' = ψ''u'' and ''w'' = (1 − ψ)''u'' are treated separately, ''v'' being essentially subject to usual elliptic regularity considerations for interior points while ''w'' requires special treatment near the boundary using difference quotients. Once the strong properties are established in terms of ∆ and the Neumann boundary conditions, the "bootstrap" regularity results can be proved exactly as for the Dirichlet problem. | |||
'''Interior estimates.''' The function ''v'' = ψ''u'' lies in H<sup>1</sup><sub>0</sub>(Ω<sub>1</sub>) where Ω<sub>1</sub> is a region with closure in Ω. If''f'' is in C<sup>∞</sup><sub>''c''</sub>(Ω) and ''g'' in C<sup>∞</sup>(Ω<sup>−</sup>) | |||
:<math>\displaystyle{(Lf,g) = (\Delta f,g)_\Omega.}</math> | |||
By continuity the same holds with ''f'' replaced by ''v'' and hence ''Lv'' = ∆''v''. So | |||
:<math>\displaystyle{\Delta v= Lv=L(\psi u) =\psi Lu +[L,\psi]u=\psi(f-u) +[\Delta,\psi]u.}</math> | |||
Hence regarding ''v'' as an element of H<sup>1</sup>('''T'''<sup>2</sup>), ∆''v'' lies in L<sup>2</sup>('''T'''<sup>2</sup>). Hence ''v'' lies in H<sup>2</sup>('''T'''<sup>2</sup>). Since ''v'' = φ ''v'' for a smooth function of compact support in Ω, ''v'' lies in H<sup>2</sup><sub>0</sub>(Ω). Moreover | |||
:<math>\displaystyle{\|v\|_{(2)}^2=\|\Delta v\|^2 + 2\|v\|_{(1)}^2,}</math> | |||
so that | |||
:<math>\displaystyle{\|v\|_{(2)} \le C( \|\Delta(v)\|+ \|v\|_{(1)}).}</math> | |||
'''Boundary estimates. ''' The function ''w'' = (1 − ψ)''u'' is supported in a collar contained in a tubular neighbourhood of the boundary. The difference quotients δ<sub>''h''</sub> ''w'' can be formed for the flow ''S''<sub>''t''</sub> and lie in H<sup>1</sup>(Ω), so the first inequality is applicable: | |||
:<math>\|\delta_h w\|_{(1)} \le \|L \delta_h w\|_{(-1)} + \|\delta_h w\|_{(0)} \le \|[L, \delta_h] w\|_{(-1)} +\|\delta_h Lw\|_{(-1)} + \| \delta_h w\|_{(0)}\le\|[L, \delta_h] w\|_{(-1)} +C\|Lw\|_{(0)} + C\| w\|_{(1)}.</math> | |||
The commutators [''L'',δ<sub>''h''</sub>] are uniformly bounded as operators from H<sup>1</sup>(Ω) to H<sup>−1</sup><sub>0</sub>(Ω). This is equivalent to checking the inequality | |||
:<math>\displaystyle{|([L,\delta_h]g,h)|\le A\|g\|_{(1)}\|h\|_{(1)},}</math> | |||
for ''g'', ''h'' smooth functions on a collar. This can be checked directly on an annulus, using invariance of Sobolev spaces under dffeomorphisms and the fact that for the annulus the commutator of δ<sub>''h''</sub> with a differential operator is obtained by applying the difference operator to the coefficients after having applied ''R''<sub>''h''</sub> to the function:<ref>{{harvnb|Folland|1995|pp=255–260}}</ref> | |||
:<math>\displaystyle{[\delta^h,\sum a_\alpha \partial^\alpha]=(\delta^h(a_\alpha)\circ R_h) \partial^\alpha.}</math> | |||
Hence the difference quotients δ<sub>''h''</sub> ''w'' are uniformly bounded, and therefore ''Y'' ''w'' lies in H<sup>1</sup>(Ω) with | |||
:<math>\displaystyle{\|Y w\|_{(1)} \le C\|L w\|_{(0)} + C^\prime \|w\|_{(1)}.}</math> | |||
Hence ''V'' ''w'' lies in H<sup>1</sup>(Ω) and ''Vw'' satisfies a similar inequality to ''Yw'': | |||
:<math>\displaystyle{\|V w\|_{(1)} \le C^{\prime\prime}(\|L w\|_{(0)} + \|w\|_{(1)}).}</math> | |||
Let ''W'' be the orthogonal vector field. As for the Dirichlet problem, to show that ''w'' lies in H<sup>2</sup>(Ω), it suffices to show that ''Ww'' lies in H<sup>1</sup>(Ω). | |||
To check this, it is enough to show that ''VWw'' and ''W''<sup>2</sup>''u'' lie in L<sup>2</sup>(Ω). As before | |||
:<math>\displaystyle{A=\Delta - V^2 - W^2,\,\,\, B=[V,W],}</math> | |||
are vector fields. On the other hand (''Lw'',φ) = (∆''w'',φ) for φ smooth of compact support in Ω, so that ''Lw'' and ∆''w'' define the same distribution on Ω. Hence | |||
:<math>\displaystyle{(W^2w,\varphi)=(L w - V^2w - Au,\varphi),\,\,\,\,\, (VWw,\varphi) =(WVw + Bw,\varphi).}</math> | |||
Since the terms on the right hand side are pairings with functions in L<sup>2</sup>(Ω), the regularity criterion shows that ''Ww'' lies in H<sup>2</sup>(Ω). Hence ''Lw'' = ∆''w'' since both terms lie in L<sup>2</sup>(Ω) and have the same inner products with φ's. | |||
Moreover the inequalities for ''Vw'' show that | |||
:<math>\|Ww\|_{(1)} \le C(\|VWw\|_{(0)} + \|W^2w\|_{(0)}) | |||
\le C\|(\Delta - V^2 -A)w\|_{(0)} + C \|(WV+B)w\|_{(0)} \le C_1 \|L w\|_{(0)} + C_1 \|w\|_{(1)}.</math> | |||
Hence | |||
:<math>\displaystyle{\|w\|_{(2)} \le C(\|V w\|_{(1)} + \|W w\|_{(1)}) \le C^\prime \|\Delta w\|_{(0)} + C^\prime \|w\|_{(1)}.}</math> | |||
It follows that ''u'' = ''v'' + ''w'' lies in H<sup>2</sup>(Ω). Moreover | |||
:<math>\|u\|_{(2)} \le C(\|\Delta v\| +\|\Delta w\| + \|v\|_{(1)} + \|w\|_{(1)})\le C^\prime(\|\psi\Delta u\| + \|(1-\psi)\Delta u\| + 2\|[\Delta,\psi]u\| +\|u\|_{(1)}) \le C^{\prime\prime} (\|\Delta u\| + \|u\|_{(1)}).</math> | |||
'''Neumann boundary conditions.''' Since ''u'' lies in H<sup>2</sup>(Ω), Green's theorem is applicable by continuity. Thus for ''v'' in H<sup>1</sup>(Ω), | |||
:<math>(f,v)=(Lu,v) + (u,v) = (u_x,v_x) + (u_y,v_y) +(u,v) =((\Delta+I)u,v) +(\partial_{n} u,v)_{\partial\Omega} | |||
=(f,v) + (\partial_{n} u,v)_{\partial\Omega}.</math> | |||
Hence the Neumann boundary conditions are satisfied: | |||
:<math>\displaystyle{\partial_n u|_{\partial \Omega} =0,}</math> | |||
where the left hand side is regarded as an element of H<sup>½</sup>(∂Ω) and hence L<sup>2</sup>(∂Ω). | |||
===Regularity of strong solutions=== | |||
The main result here states that if ''u'' lies in H<sup>''k''+1</sup> with ''k'' ≥ 1, ∆''u'' in H<sup>''k''</sup> and ∂<sub>''n''</sub>''u'' = 0 on ∂Ω, then ''u'' lies in H<sup>''k''+2</sup> and | |||
:<math>\displaystyle{\|u\|_{(k+2)} \le C\|\Delta u\|_{(k)} + C \|u\|_{(k+1)},}</math> | |||
for some constant independent of ''u''. | |||
Like the ocrresponding result for the Dirichlet problem, this is proved by induction on ''k'' ≥ 1. For ''k'' = 1, ''u'' is also a weak solution of the Neumann problem so satisfies the estimate above for ''k'' = 0. The Neumann boundary condition can be written | |||
:<math>\displaystyle{Zu|_{\partial\Omega}=0.}</math> | |||
Since ''Z'' commutes with the vector field ''Y'' corresponding to the period flow ''S''<sub>''t''</sub>, the inductive method of proof used for the Dirichlet problem works equally well in this case: for the difference quotients δ<sup>''h''</sup> preserve the boundary condition when expressed in terms of ''Z''.<ref>{{harvnb|Taylor|2011|p=348}}</ref> | |||
'''Smoothness of eigenfunctions.''' It follows by induction from the regularity theorem for the Neumann problem that the eigenfunctions of ''D'' in H<sup>1</sup>(Ω) lie in C<sup>∞</sup>{Ω<sup>−</sup>). Moreover any solution of ''Du'' = ''f'' with ''f'' in C<sup>∞</sup>{Ω<sup>-</sup>) and ''u'' in H<sup>1</sup>(Ω) must have ''u'' in C<sup>∞</sup>{Ω<sup>-</sup>). In both cases by the vanishing properties, the normal derivatives of the eigenfunctions and ''u'' vanish on ∂Ω. | |||
'''Solving the associated Neumann problem.''' The method above can be used to solve the associated Neumann boundary value problem: | |||
:<math>\displaystyle{\Delta f|_\Omega = 0,\,\, \partial_n f|_{\partial\Omega} =g,}</math> | |||
with ''g'' a smooth function on ∂Ω. By Borel's lemma ''g'' is the restriction of a function ''G'' in C<sup>∞</sup>(Ω<sup>−</sup>). Let ''F'' be a smooth function such that ∂<sub>''n''</sub>''F'' = ''G'' near the boundary. Let ''u'' be the solution of ∆''u'' = −∆''F'' with ∂<sub>''n''</sub>''u'' = 0. Then ''f'' = ''u'' + ''F'' solves the boundary value problem.<ref>{{harvnb|Folland|1995|p=85}}</ref> | |||
==Notes== | |||
{{reflist|2}} | |||
==References== | |||
*{{citation|last=John|first= Fritz|title=Partial differential equations|edition=4th|series= Applied Mathematical Sciences|volume= 1|publisher= Springer-Verlag|year= 1982|isbn= 0-387-90609-6}} | |||
*{{citation|last=Bers|first=Lipman|last2=John|first2=Fritz|last3= Schechter|first3= Martin|title=Partial differential equations, with supplements by Lars Gȧrding and A. N. Milgram|series= Lectures in Applied Mathematics|volume= 3A|publisher= American Mathematical Society|year=1979|isbn=0-8218-0049-3}} | |||
*{{citation|title=Lectures on Elliptic Boundary Value Problems|first=Shmuel|last= Agmon|authorlink=Shmuel Agmon|year=2010|publisher=American Mathematical Society|isbn=0-8218-4910-7}} | |||
* {{citation|first=Elias M.|last= Stein|authorlink=Elias Stein|year=1970|title=Singular Integrals and Differentiability Properties of Functions|publisher=Princeton University Press}} | |||
*{{citation|last=Greene|first= Robert E.|last2= Krantz|first2= Steven G.|title= Function theory of one complex variable|edition=3rd|series= Graduate Studies in Mathematics|volume= 40|publisher= American Mathematical Society|year= 2006|isbn= 0-8218-3962-4}} | |||
*{{citation| last=Taylor|first= Michael E.|authorlink=Michael E. Taylor|title= Partial differential equations I. Basic theory|edition=2nd |series= Applied Mathematical Sciences|volume= 115|publisher=Springer|year=2011|isbn= 978-1-4419-70}} | |||
*{{citation|last=Zimmer|first= Robert J.|title= Essential results of functional analysis|series= Chicago Lectures in Mathematics|publisher= University of Chicago Press|year= 1990|isbn= 0-226-98337-4}} | |||
*{{citation|last=Folland|first= Gerald B.|title= Introduction to partial differential equations|edition=2nd|publisher=Princeton University Press|year=1995|isbn= 0-691-04361-2}} | |||
*{{citation|title=Introduction to the Theory of Linear Partial Differential Equations|volume=14|series= Studies in Mathematics and Its Applications|first=Jacques|last= Chazarain|first2= Alain|last2= Piriou|publisher=Elsevier|year= 1982|isbn=0444864520}} | |||
*{{citation|last=Bell|first=Steven R.|title= The Cauchy transform, potential theory, and conformal mapping|series= Studies in Advanced Mathematics|publisher= CRC Press|year= 1992|isbn=0-8493-8270-X}} | |||
*{{citation|title=Foundations of Differentiable Manifolds and Lie Groups|series=Graduate Texts in Mathematics|volume= 94|year=1983| | |||
first=Frank W.|last= Warner|isbn=0387908943|publisher=Springer}} | |||
*{{citation|title=Principles of Algebraic Geometry|first=Phillip |last=Griffiths|first2= Joseph|last2= Harris|publisher= Wiley Interscience| year=1994|isbn=0471050598}} | |||
*{{citation|last=Courant|first= R.|title=Dirichlet's Principle, Conformal Mapping, and Minimal Surfaces| | |||
publisher=Interscience|year= 1950}} | |||
*{{citation|last=Schiffer|first= M.|last2=Hawley|first2= N. S.|title=Connections and conformal mapping|journal= | |||
Acta Math.|volume= 107|year= 1962|pages= 175–274}} | |||
*{{citation|first=Lars|last= Hörmander|authorlink=Lars Hörmander|title=The analysis of linear partial differential operators, I. Distribution theory and Fourier analysis|edition=2nd|publisher= Springer-Verlag|year=1990|isbn= 3-540-52343-X}} | |||
*{{citation|title=An Introduction to Partial Differential Equations|volume =13|series= Texts in Applied Mathematics|first=Michael|last= Renardy|first2= Robert C.|last2= Rogers|edition=2nd |publisher=Springer|year= 2004|isbn=0387004440}} | |||
[[Category:Partial differential equations]] | |||
[[Category:Harmonic analysis]] | |||
[[Category:Operator theory]] | |||
[[Category:Functional analysis]] |
Revision as of 23:45, 14 November 2013
In mathematics, Sobolev spaces for planar domains are one of the principal techniques used in the theory of partial differential equations for solving the Dirichlet and Neumann boundary value problems for the Laplacian in a bounded domain in the plane with smooth boundary. The methods use the theory of bounded operators on Hilbert space. They can be used to deduce regularity properties of solutions and to solve the corresponding eigenvalue problems.
Sobolev spaces with boundary conditions
Let Ω be a bounded domain in R2 with smooth boundary. Since Ω is contained in a large square in R2, it can be regarded as a domain in T2 by identifying opposite sides of the square. The theory of Sobolev spaces on T2 can be found in Template:Harvtxt, an account which is followed in several later textbooks such as Template:Harvtxt and Template:Harvtxt.
For k an integer, the (restricted) Sobolev space Hk0(Ω) is defined as the closure of C∞c(Ω) in the standard Sobolev space Hk(T2).
- For k = 0, H00(Ω) equals L2(Ω).
- Vanishing properties on boundary: For k > 0 the elements of Hk0(Ω) are referred to as "L2 functions on Ω which vanish with their first k − 1 derivatives on the boundary."[1] In fact if
- agrees with a function in Hk0(Ω), then g = ∂α f is in C1. Let fn be smooth functions of compact support in Ω tending to f in the Sobolev norm and set gn = ∂α fn. Thus gn tends towards g in H10(Ω). Hence for h in C∞(T2) and D = a ∂x +b ∂y,
- By Green's theorem this implies
- where k = h cos n ⋅ (a,b) with n the unit normal to the boundary. Since such k form a dense subspace of L2(Ω), it follows that g = 0 on the boundary.
- Support properties: Let Ωc be the complement of the closure of Ω and define restricted Sobolev spaces analogously for Ωc. Both sets of spaces have a natural pairing with C∞(T2). The Sobolev space for Ω is the annihilator in the Sobolev space for T2 of C∞c(Ωc) and that for Ωc is the annihilator of C∞c(Ω).[2] In fact this is proved by locally applying a small translation to move the domain inside itself and then smoothing by a smooth convolution operator.
- Suppose g in Hk(T2) annihilates C∞c(Ωc). By compactness, there are finitely many opens U0, U1, ... , UN covering the closure of Ω such that the closure of U0 is disjoint from the boundary and each Ui is an open disc about a boundary point zi such that in Ui small translations in the direction of the normal vector ni carry the closure of Ω into Ω. Add an open UN+1 with closure in Ωc to produce a cover of T2 and let ψi be a partition of unity subordinate to this cover. If translation by n is denoted by λn, then
- tend to g as t decreases to 0 and still lie in the annihilator, indeed they are in the annihilator for a larger domain than Ωc, the complement of which lies in Ω. Convolving by smooth functions of small support produces smooth approximations in the annihilator of a slightly smaller domain still with complement in Ω. These are necessarily smooth functions of compact support in Ω.
- Further vanishing properties on the boundary: The characterization in terms of annihilators shows that a Ck function f on the closure of Ω lies in Hk0(Ω) if (and only if) it and its derivatives of order less than k vanish on the boundary.[3] In fact f can be extended to T2 by setting it to be 0 on Ωc. The extension F defines as element in Hk(T2) using the formula
- and satisfies (F,g) = 0 for g in C∞c(Ωc).
- Duality: For k ≥ 0, define H−k(Ω) to be the orthogonal complement in H−k(T2) of H−k0(Ωc). Let Pk be the orthogonal projection onto H−k(Ω), so that Qk = I - Pk is the orthogonal projection onto H−k0(Ωc). When k = 0, this just gives H0(Ω) = L2(Ω). If f is in Hk0(Ω) and g in H−k(T2), then
- This implies that under the pairing between Hk(T2) and H−k(T2), Hk0(Ω) and H−k(Ω) are each other's duals.
- Approximation by smooth functions: The image of C∞c(Ω) is dense in H−k(Ω) for k ≤ 0. This is obvious for k = 0 since the sum C∞c(Ω) + C∞c(Ωc) is dense in L2(T2). Density for k < follows because the image of L2(T2) is dense in H−k(T2) and Pk annihilates C∞c(Ωc).
- Canonical isometries: The operator (I + ∆)k gives an isometry of H2k0(Ω) into H0(Ω) and of Hk0(Ω) onto H−k(Ω). In fact the first statement follows because it is true on T2. That (I + ∆)k is an isometry on Hk0(Ω) follows using the density of C∞c(Ω) in H−k(Ω): for f, g smooth of compact support on Ω
- Since the adjoint map between the duals can by identified with this map, it follows that (I + ∆)k is a unitary map.
Application to Dirichlet problem
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- Invertibility of ∆: The operator ∆ defines an isomorphism between H10(Ω) and H−1(Ω). In fact it is a Fredholm operator of index 0. The kernel of ∆ in H1(T2) consists of constant functions and none of these except zero vanish on the boundary of Ω. Hence the kernel of H10(Ω) is (0) and ∆ is invertible.
- In particular the equation ∆ f = g has a unique solution in H10(Ω) for g in H−1(Ω).
- Eigenvalue problem: Let T be the operator on L2(Ω) defined by
- where R0 is the inclusion of L2(Ω) in H−1(Ω) and R1 of H10 in L2(Ω), both compact operators by Rellich's theorem. The operator T is compact, self-adjoint and with (Tf,f) > 0 for all f. By the spectral theorem, there is a complete orthonormal set of eigenfunctions fn in L2(Ω) with
- Since μn > 0, fn lies in H10(Ω). Setting λn = 1/ μn, the fn are eigenfunctions of the Laplacian:
Sobolev spaces without boundary condition
To determine the regularity properties of the eigenfunctions fn and solutions of
enlargements of the Sobolev spaces Hk0(Ω) have to be considered. Let C∞(Ω−) be the space of smooth functions on Ω which with their derivatives extend continuously to the closure of Ω. By Borel's lemma, these are precisely the restrictions of smooth functions on T2. The Sobolev space Hk(Ω) is defined to the Hilbert space completion of this space for the norm
This norm agrees with the Sobolev norm on C∞c(Ω) so that Hk0(Ω) can be regarded as a closed subspace of Hk(Ω). Unlike Hk0(Ω). Hk(Ω) is not naturally a subspace of Hk(T2), but the map restricting smooth functions from T2 to the closure of Ω is continuous for the Sobolev norm so extends by continuity to a map ρk of Hk(T2) into Hk(Ω).
- Invariance under diffeomorphism: Any diffeomorphism between the closures of two smooth domains induces an isomorphism between the Sobolev space. This is a simple consequence of the chain rule for derivatives.
- Extension theorem: The restriction of ρk to the orthogonal complement of its kernel defines an isomorphism onto Hk(Ω). The extension map Ek is defined to be the inverse of this map: it is an isomorphism (not necessarily norm preserving) of Hk(Ω) onto the orthogonal complement of Hk0(Ωc) such that ρk ∘ Ek = I. On C∞c(Ω), it agrees with the natural inclusion map. Bounded extension maps Ek of this kind from Hk(Ω) to Hk(T2) were constructed first constructed by Hestenes and Lions. For smooth curves the Seeley extension theorem provides an extension which is continuous in all the Sobolev norms. A version of the extension which applies in the case where the boundary is just a Lipschitz curve was constructed by Calderón using singular integral operators and generalized by Template:Harvtxt.
- It is sufficient to construct an extension E for a neighbourhood of a closed annulus, since a collar around the boundary is diffeomorphic to an annulus I x T with I a closed interval in T. Taking a smooth bump function ψ with 0 ≤ ψ ≤ 1, equal to 1 near the boundary and 0 outside the collar, E( ψf) + (1- ψ)f will provide an extension on Ω. On the annulus, the problem reduces to finding an extension for Ck(I) in Ck(T). Using a partition of unity the task of extending reduces to a neighbourhood of the end points of I. Assuming 0 is the left end point, an extension is given locally by
- Matching the first derivatives of order k or less at 0, gives
- This matrix equation is solvable because the determinant is non-zero by Vandermonde's formula. It is straightforward to check that the formula for E(f), when appropriately modified with bump functions, leads to an extension which is continuous in the above Sobolev norm.[4]
- Restriction theorem: The restriction map ρk is surjective with ker ρk = Hk0(Ωc). This is an immediate consequence of the extension theorem and the support properties for Sobolev spaces with boundary condition.
- Duality: Hk(Ω) is naturally the dual of H−k0(Ω). Again this is an immediate consequence of the restriction theorem. Thus the Sobolev spaces form a chain:
- The differentiation operators ∂x, ∂y carry each Sobolev space into the larger one with index 1 less.
- Sobolev embedding theorem: Hk+2(Ω) is contained in Ck(Ω−). This is an immediate consequence of the extension theorem and the Sobolev embedding theorem for Hk+2(T2).
- Characterization: Hk(Ω) consists of f in L2(Ω) = H0(Ω) such that all the derivatives ∂αf lie in L2(Ω) for |α| ≤ k.Here the derivatives are taken within the chain of Sobolev spaces above.[5] Since C∞c(Ω) is weakly dense in Hk(Ω), this condition is equivalent to the existence of L2 functions fα such that
- for |α| ≤ k and φ in C∞c(Ω).
- To prove the characterization, note that if f is in Hk(Ω), then ∂αf lies in Hk−|α|(Ω) and hence in H0(Ω) = L2(Ω). Conversely the result is well-known for the Sobolev spaces Hk(T2): the assumption implies that the (∂x -i∂y)k f is in L2(T2) and the corresponding condition on the Fourier coefficients of f shows that f lies in Hk(T2). Similarly the result an be proved directly for an annulus [−δ,δ] x T. In fact by the argument on T2 the restriction of f to any smaller annulus [−δ',δ'] x T lies in Hk: equivalently the restriction of the function fR(x,y) = f(Rx,y) lies in Hk for R > 1. On the other hand ∂αfR tends to ∂αf in L2 as R tends to 1, so that f must lie in Hk. The case for a general domain Ω reduces to these two cases since f can be written as f = ψf + (1 − ψ)f with ψ a bump function supported in Ω such that 1 − ψ is supported in a collar of the boundary.
- Regularity theorem: If f in L2(Ω) has both derivatives ∂xf and ∂yf in Hk(Ω) then f lies in Hk+1(Ω). This is an immediate consequence of the characterization of Hk(Ω) above. In fact if this is true even when satisfied at the level of distributions: if there are functions g, h in Hk(Ω) such that (g,φ) = (f,φx) and (h,φ) = (f,φy) for φ in C∞c(Ω), then f is in Hk+1(Ω).
- Rotations on an annulus: For an annulus I x T, the extension map to T2 is by construction equivariant with respect to rotations in the second variable,
- On T2 it is known that if f is in Hk, then the difference quotient δhf = h−1(Rhf - f) tends to ∂y f in Hk−1; if the difference quotients are bounded in Hk then ∂y f lies in Hk. Both assertions are consequences of the formula:
- These results on T2 imply analogous results on the annulus using the extension.
Regularity for Dirichlet problem
- Regularity for dual Dirichlet problem: If ∆u = f with u in H10(Ω) and f in Hk−1(Ω) with k ≥ 0, then u lies in Hk+1(Ω).
- Take a decomposition u = ψu + (1 − ψ)u with ψ supported in Ω and 1 − ψ supported in a collar of the boundary. Standard Sobolev theory for T2 can be applied to ψu: elliptic regularity implies that it lies in Hk+1(T2) and hence Hk+1(Ω). v = (1 − ψ)u lies in H10 of a collar, diffeomorphic to an annulus, so it suffices to prove the result with Ω a collar and ∆ replaced by
- The proof[6] proceeds by induction on k, proving simultaneously the inequality
- for some constant C depending only on k. It is straightforward to establish this inequality for k = 0, where by density u can be taken to be smooth of compact support in Ω:
- The collar is diffeomorphic to an annulus. The rotational flow Rt on the annulus induces a flow St on the collar with corresponding vector field Y = r ∂x + s ∂y. Thus Y corresponds to the vector field ∂θ. The radial vector field on the annulus r∂r is a commuting vector field which on the collar gives a vector field Z = p ∂x + q ∂y proportional to the normal vector field. The vector fields Y and Z commute.
- The difference quotients δh u can be formed for the flow St. The commutators [δh,∆1] are second order differential operators from Hk+1(Ω) to Hk−1(Ω). Their operators norms are uniformly bounded for h near 0; for the computation can be carried out on the annulus where the commutator just replaces the coefficients of ∆1 by their difference quotients composed with Sh. On the other hand v = δh u lies in H10(Ω), so the inequalities for u apply equally well for v:
- The uniform boundedness of the difference quotients δh u implies that Y u lies in Hk+1(Ω) with
- It follows that V u lies in Hk+1(Ω) where V is the vector field
- where a2 + b2 = 1. Moreover Vu satisfies a similar inequality to Yu.
- Let W be the orthogonal vector field
- It can also be written as ξZ for some smooth nowhere vanishing function ξ on a neighbourhood of the collar.
- It suffices to show that Wu lies in Hk+1(Ω). For then
- so that ∂xu and ∂yu lie in Hk+1(Ω) and u must lie in Hk+2(Ω).
- To check the result on Wu, it is enough to show that VWu and W2u lie in Hk(Ω). Note that
- are vector fields. But then
- with all terms on the right hand side in Hk(Ω). Moreover the inequalities for Vu show that
- Hence
- Smoothness of eigenfunctions. It follows by induction from the regularity theorem for the dual Dirichlet problem that the eigenfunctions of ∆ in H10(Ω) lie in C∞{Ω−). Moreover any solution of ∆u = f with f in C∞{Ω-) and u in H10(Ω) must have u in C∞{Ω-). In both cases by the vanishing properties, the eigenfunctions and u vanish on the boundary of Ω.
- Solving the Dirichlet problem. The dual Dirichlet problem can be used to solve the Dirichlet problem:
- with g a smooth function on ∂Ω. By Borel's lemma g is the restriction of a function G in C∞(Ω−). Let F be the smooth solution of ∆F = ∆G with F = 0 on ∂Ω. Then f = G − F solves the Dirichlet problem. By the maximal principle, the solution is unique.[7]
Application to smooth Riemann mapping theorem
The solution to the Dirichlet problem can be used to prove a strong form of the Riemann mapping theorem for simply connected domains with smooth boundary. The method also applies to a region diffeomorphic to an annulus.[8] For multiply connected regions with smooth boundary Template:Harvtxt have given a method for mapping the region onto a disc with circular holes. Their method involves solving the Dirichlet problem with a non-linear boundary condition. They construct a function g harmonic in the interior of Ω with
on ∂Ω, where κ is the curvature of the boundary curve, ∂n is the derivative in the direction of the normal to ∂Ω and K is constant on each boundary component.
Template:Harvtxt gives a proof of the Riemann mapping theorem for a simply connected domain Ω with smooth boundary. Translating if necessary, it can be assumed that 0 lies in Ω. The solution of the Dirichlet problem shows that there is a unique smooth function U(z) on the closure of Ω which is harmonic in Ω and equal to −log |z| on the boundary. Define the Green's function by G(z) = log |z| + U(z). It vanishes on the boundary and is harmonic on Ω away from 0. The harmonic conjugate V of U is the unique real function on Ω such that U + i V is holomorphic. As such it must satisfy the Cauchy-Riemann equations:
The solution is given by
where the integral is taken over any path in the closure of Ω. It is easily verified that Vx and Vy are exist and are given by the corresponding derivatives of U. Thus V is a smooth function on the closure of Ω, vanishing at 0. By the Cauchy-Riemann f = U + i V is smooth on the closure of Ω, holomorphic on Ω and f(0) = 0. The function H = arg z + V(z) is only defined up to multiples of 2π, but the function
is a holomorphic on Ω and smooth on its closure. By construction it satisfies F(0) = 0 and |F(z)| = 1 for z on the boundary of Ω. Since z has winding number 1, so too does F(z). On the other hand F(z) = 0 only for z =0 where there is a simple zero. So by the argument principle F assumes every value in the unit disc exactly once and F ' does not vanish inside Ω. To check that the derivative on the boundary curve is non-zero amounts to computing the derivative of eiH, i.e. the derivative of H should not vanish on the boundary curve. By the Cauchy-Riemann equations these tangential derivative are up to a sign the directional derivative in the direction of the normal to the boundary. But G vanishes on the boundary and is strictly negative in Ω since |F| = eG. The Hopf lemma implies that the directional derivative of G in the direction of the outward normal is strictly positive. So on the boundary curve F has nowhere vanishing derivative. Since the boundary curve has winding number one, F defines a diffeomorphism of the boundary curve onto the unit circle. Accordingly F is a smooth diffeomorphism of the closure of Ω onto the closed unit disk, which restricts to a holomorphic map of Ω onto the open unit disk and a smooth diffeomorphism between the boundaries.
Similar arguments can be applied to prove the Riemann mapping theorem for a doubly connected domain Ω bounded by simple smooth curves Ci (the inner curve) and Co (the outer curve). B tranlsating we can assume 1 lies on the outer boundary. Let u be the smooth solution of the Dirichlet problem with U = 0 on the outer curve and −1 on the inner curve. By the maximum principle 0 < u(z) < 1 for z in Ω and so by the Hopf lemma the normal derivatives of u are negative on the outer curve and positive on the inner curve. The integral of −uy dx + uy dx over the boundary is zero by Stoke's theorem so the contributions from the boundary curves cancel. On the other hand on each boundary curve the contribution is the integral of the normal derivative along the boundary. So there is a constant c > 0 such that U = cu satisfies
on each boundary curve. The harmonic conjugate V of U can again be defined by
and is well-defined up to multiples of 2π. The function
is smooth on the closure of Ω and holomorphic in Ω. On the outer curve |F| = 1 and on the inner curve |F| = e−c = r < 1. The tangential derivatives on the outer curves are nowhere vanishing by the Cauchy-Riemann equations, since the normal derivatives are nowhere vanishing. The normalization of the integrals implies that F restricts to a diffeonmorphism between the boundary curves and the two concentric circles. Since the images of outer and inner curve have winding number 1 and 0 about any point in the annulus, an application of the argument principle implies that F assumes every value within the annulus r < |z| < 1 exactly once; since that includes mutliplicities, the complex derivative of F is nowhere vanishing in Ω. This F is a smooth diffeomorphism of the closure of Ω onto the closed annulus r ≤ |z| ≤ 1, restricting to a holomorphic map in the interior and a smooth diffeomorphism on both boundary curves.
Trace map
The restriction map τ of C∞(T2) onto C∞(T) = C∞(1 × T) extends to a continuous map Hk(T2) into Hk − ½(T) for k ≥ 1.[9] In fact
so the Cauchy–Schwarz inequality yields
where, by the integral test,
The map τ is onto since a continuous extension map E can be constructed from Hk − ½(T) to Hk(T2).[10][11] In fact set
where
Thus λn > ck. If g is smooth, then by construction Eg restricts to g on 1 × T. Moreover E is a bounded linear map since
It follows that there is a trace map τ of Hk(Ω) onto Hk − ½(∂Ω). Indeed take a tubular neighbourhood of the boundary and a smooth function ψ supported in the collar and equal to 1 near the boundary. Multiplication by ψ carries functions into Hk of the collar, which can be identified with Hk of an annulus for which there is a trace map. The invariance under diffeomorphims (or coordinate change) of the half-integer Sobolev spaces on the circle follows from the fact that an equivalent norm on Hk + ½(T) is given by[12]
It is also a consequence of the properties of τ and E (the "trace theorem").[13] In fact any diffeomorphism f of T induces a diffeomorphism F of T2 by acting only on the second factor. Invariance of Hk(T2) under the induced map F* therefore implies invariance of Hk − ½(T) under f*, since f* = τ ∘ F* ∘ E.
Further consequences of the trace theorem are the two exact sequences[14][15]
and
where the last map takes f in H2(Ω) to f|∂Ω and ∂nf|∂Ω. There are generalizations of these sequences to Hk(Ω) involving higher powers of the normal derivative in the trace map:
The trace map to Hj − ½(∂Ω) takes f to ∂nk − jf|∂Ω
Abstract formulation of boundary value problems
The Sobolev space approach to the Neumann problem cannot be phrased quite as directly as that for the Dirichlet problem. The main reason is that for a function f in H1(Ω), the normal derivative ∂nf|∂Ω cannot be a priori defined at the level of Sobolev spaces. Instead an alternative formulation of boundary value problems for the Laplacian Δ on a bounded region Ω in the plane is used. It employs Dirichlet forms, sesqulinear bilinear forms on H1(Ω), H10 or an intermediate closed subspace. Integration over the boundary is not involved in defining the Dirichlet form. Instead, if the Dirichlet form satisfies a certain positivity condition, termed coerciveness, solution can be shown to exist in a weak sense, so-called "weak solutions". A general regularity theorem than implies that the solutions of the boundary value problem must lie in H2(Ω), so that they are strong solutions and satisfy boundary conditions involving the restriction of a function and its normal derivative to the boundary. The Dirichlet problem can equally well be phrased in these terms, but because the trace map f|∂Ω is already defined on H1(Ω), Dirichlet forms do not need to be mentioned explicitly and the operator formulation is more direct. A unified discussion is given in Template:Harvtxt and briefly summarised below. It is explained how the Dirichlet problem, as discussed above, fits into this framework. Then a detailed treatment of the Neumann problem from this point of view is given following Template:Harvtxt.
The HIlbert space formulation of boundary value problems for the Laplacian Δ on a bounded region Ω in the plane proceeds from the following data:[16]
- A closed subspace H lying between H10(Ω) and H1(Ω)
- A Dirichlet form for Δ given by a bounded Hermitian bilinear form D(f,g) defined for f, g in H1(Ω) such that D(f,g)=(∆ f,g) for f, g in H10(Ω).
- D is coercive, i.e. there is a positive constant C and a non-negative constant λ such that D(f,f) ≥ C (f,f)(1) − λ(f,f).
A weak solution of the boundary value problem given initial data f in L2(Ω) is a function u in H such that
for all g in H.
For both the Dirichlet and Neumann problem
For the Dirichlet problem H = H10(Ω). In this case
for f, g in H. By the trace theorem the solution satisfies u|Ω = 0 in H½(∂Ω).
For the Neumann problem H is taken to be H1(Ω).
Application to Neumann problem
The classical Neumann problem on Ω consists in solving the boundary value problem
with f in C∞(Ω−) and u in C∞(Ω−) and satisfying the Neumann boundary condition
Green's theorem implies that for u, v in C∞(Ω−)
Thus if Δu = 0 in Ω and satisfies the Neumann boundary conditions, ux, uy = 0, and so u is constant in Ω.
Hence the Neumann problem has a unique solution up to adding constants.[17]
Consider the Hermitian form on H1(Ω) defined by
Since H1(Ω) is in duality with H−10(Ω), there is a unique element Lu in H−10(Ω) such that
The map I + L is an isometry of H1(Ω) onto H−10(Ω), so in particular L is bounded.
In fact
So
On the other hand any f in H−10(Ω) defines a bounded conjugate-linear form on H1(Ω) sending v to (f,v). By the Riesz–Fischer theorem, there exists u in H1(Ω) such that
Hence (L + I)u = f and so L + I is surjective. Define a bounded linear operator T on L2(Ω) by
where R1 is the map H1(Ω) → L2(Ω), a compact operator, and R0 is the map L2(Ω) → H−10(Ω), its adjoint, so also compact.
The operator T has the following properties:
- T is a contraction since it is a composition of contractions
- T is compact, since R0 and R1 are compact by Rellich's theorem
- T is self-adjoint, since if f and g are in L2(Ω), they can be written f =(L + I)u, g = (L + I)v with u, v in H1(Ω) so
- T has positive spectrum and kernel (0), for
- and Tf = 0 implies u = 0 and hence f = 0.
- There is a complete orthonormal basis fn of L2(Ω) consisting of eigenfunctions of T. Thus
- with 0 < μn ≤ 1 and μn decreasing to 0.
- The eigenfunctions all lie in H1(Ω) since the image of T lies in H1(Ω).
- The fn are eigenfunctions of L with
- Thus λn are non-negative and increase to ∞.
- The eigenvalue 0 occurs with multiplicity one and corresponds to the constant function. For if u in H1(Ω) satisfies Lu = 0, then
- so u is constant.
Regularity for Neumann problem
Weak solutions are strong solutions
The first main regularity result shows that a weak solution expressed in terms of the operator L and the Dirichlet form D is a strong solution in the classical sense, expressed in terms of the Laplacian Δ and the Neumann boundary conditions. Thus if u = Tf with u in H1(Ω) and f in L2(Ω), then u in fact lies in H2(Ω), satisfies Δu + u = f and ∂nu|∂Ω = 0. Moreover for some constant C independent of u,
Note that
since
Take a decomposition u = ψu + (1 − ψ)u with ψ supported in Ω and 1 − ψ supported in a collar of the boundary.
The operator L is characterized by
for f, g in C∞(Ω−). Then
so that
The function v = ψu and w = (1 − ψ)u are treated separately, v being essentially subject to usual elliptic regularity considerations for interior points while w requires special treatment near the boundary using difference quotients. Once the strong properties are established in terms of ∆ and the Neumann boundary conditions, the "bootstrap" regularity results can be proved exactly as for the Dirichlet problem.
Interior estimates. The function v = ψu lies in H10(Ω1) where Ω1 is a region with closure in Ω. Iff is in C∞c(Ω) and g in C∞(Ω−)
By continuity the same holds with f replaced by v and hence Lv = ∆v. So
Hence regarding v as an element of H1(T2), ∆v lies in L2(T2). Hence v lies in H2(T2). Since v = φ v for a smooth function of compact support in Ω, v lies in H20(Ω). Moreover
so that
Boundary estimates. The function w = (1 − ψ)u is supported in a collar contained in a tubular neighbourhood of the boundary. The difference quotients δh w can be formed for the flow St and lie in H1(Ω), so the first inequality is applicable:
The commutators [L,δh] are uniformly bounded as operators from H1(Ω) to H−10(Ω). This is equivalent to checking the inequality
for g, h smooth functions on a collar. This can be checked directly on an annulus, using invariance of Sobolev spaces under dffeomorphisms and the fact that for the annulus the commutator of δh with a differential operator is obtained by applying the difference operator to the coefficients after having applied Rh to the function:[18]
Hence the difference quotients δh w are uniformly bounded, and therefore Y w lies in H1(Ω) with
Hence V w lies in H1(Ω) and Vw satisfies a similar inequality to Yw:
Let W be the orthogonal vector field. As for the Dirichlet problem, to show that w lies in H2(Ω), it suffices to show that Ww lies in H1(Ω).
To check this, it is enough to show that VWw and W2u lie in L2(Ω). As before
are vector fields. On the other hand (Lw,φ) = (∆w,φ) for φ smooth of compact support in Ω, so that Lw and ∆w define the same distribution on Ω. Hence
Since the terms on the right hand side are pairings with functions in L2(Ω), the regularity criterion shows that Ww lies in H2(Ω). Hence Lw = ∆w since both terms lie in L2(Ω) and have the same inner products with φ's.
Moreover the inequalities for Vw show that
Hence
It follows that u = v + w lies in H2(Ω). Moreover
Neumann boundary conditions. Since u lies in H2(Ω), Green's theorem is applicable by continuity. Thus for v in H1(Ω),
Hence the Neumann boundary conditions are satisfied:
where the left hand side is regarded as an element of H½(∂Ω) and hence L2(∂Ω).
Regularity of strong solutions
The main result here states that if u lies in Hk+1 with k ≥ 1, ∆u in Hk and ∂nu = 0 on ∂Ω, then u lies in Hk+2 and
for some constant independent of u.
Like the ocrresponding result for the Dirichlet problem, this is proved by induction on k ≥ 1. For k = 1, u is also a weak solution of the Neumann problem so satisfies the estimate above for k = 0. The Neumann boundary condition can be written
Since Z commutes with the vector field Y corresponding to the period flow St, the inductive method of proof used for the Dirichlet problem works equally well in this case: for the difference quotients δh preserve the boundary condition when expressed in terms of Z.[19]
Smoothness of eigenfunctions. It follows by induction from the regularity theorem for the Neumann problem that the eigenfunctions of D in H1(Ω) lie in C∞{Ω−). Moreover any solution of Du = f with f in C∞{Ω-) and u in H1(Ω) must have u in C∞{Ω-). In both cases by the vanishing properties, the normal derivatives of the eigenfunctions and u vanish on ∂Ω.
Solving the associated Neumann problem. The method above can be used to solve the associated Neumann boundary value problem:
with g a smooth function on ∂Ω. By Borel's lemma g is the restriction of a function G in C∞(Ω−). Let F be a smooth function such that ∂nF = G near the boundary. Let u be the solution of ∆u = −∆F with ∂nu = 0. Then f = u + F solves the boundary value problem.[20]
Notes
43 year old Petroleum Engineer Harry from Deep River, usually spends time with hobbies and interests like renting movies, property developers in singapore new condominium and vehicle racing. Constantly enjoys going to destinations like Camino Real de Tierra Adentro.
References
- Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010
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