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{{see also|Discrete Fourier transform (general)}} | |||
In [[mathematics]], the '''Fourier transform on finite groups''' is a generalization of the [[discrete Fourier transform]] from [[cyclic group|cyclic]] to arbitrary [[finite group]]s. | |||
==Definitions== | |||
The '''Fourier transform''' of a function <math>f : G \rightarrow \mathbb{C}\,</math> | |||
at a [[representation of a finite group|representation]] <math>\varrho : G \rightarrow GL(d_\varrho, \mathbb{C})\,</math> of <math>G\,</math> is | |||
:<math> | |||
\widehat{f}(\varrho) = \sum_{a \in G} f(a) \varrho(a). | |||
</math> | |||
So for each representation <math>\varrho\,</math> of <math>G\,</math>, <math>\widehat{f}(\varrho)\,</math> is a <math>d_\varrho \times d_\varrho\,</math> matrix, where <math>d_\varrho\,</math> is the degree of <math>\varrho\,</math>. | |||
Let <math>\varrho_i\,</math> be a complete set of inequivalent [[irreducible representation]]s of <math>G</math>. Then<!--, somehow -->, <math>|G| = \sum_i d_{\varrho_i}^2</math>. Then the '''inverse Fourier transform''' at an element <math>a\,</math> of <math>G\,</math> is given by | |||
:<math> | |||
f(a) = \frac{1}{|G|} \sum_i d_{\varrho_i} \text{Tr}\left(\varrho_i(a^{-1})\widehat{f}(\varrho_i)\right), | |||
</math> | |||
where <math>d_{\varrho_i}\,</math> is the degree of the representation <math>\varrho_i.\,</math> | |||
==Properties== | |||
===Transform of a convolution=== | |||
The '''convolution''' of two functions <math>f, g : G \rightarrow \mathbb{C}\,</math> is defined as | |||
:<math> | |||
(f \ast g)(a) = \sum_{b \in G} f(ab^{-1}) g(b). | |||
</math> | |||
The Fourier transform of a convolution at any representation <math>\varrho\,</math> of <math>G\,</math> is given by | |||
:<math> | |||
\widehat{f \ast g}(\varrho) = \widehat{f}(\varrho)\widehat{g}(\varrho). | |||
</math> | |||
===Plancherel formula=== | |||
For functions <math>f, g : G \rightarrow \mathbb{C}\,</math>, the Plancherel formula states | |||
:<math> | |||
\sum_{a \in G} f(a^{-1}) g(a) = \frac{1}{|G|} \sum_i d_{\varrho_i} \text{Tr}\left(\widehat{f}(\varrho_i)\widehat{g}(\varrho_i)\right), | |||
</math> | |||
where <math>\varrho_i\,</math> are the irreducible representations of <math>G.\,</math> | |||
==Fourier transform on finite abelian groups== | |||
Since the irreducible representations of finite [[abelian group]]s are all of degree 1 and hence equal to the irreducible characters of the group, Fourier analysis on finite abelian groups is significantly simplified. For instance, the Fourier transform yields a scalar- and not matrix-valued function. | |||
Furthermore, the irreducible characters of a group may be put in one-to-one correspondence with the elements of the group. | |||
Therefore, we may define the Fourier transform for finite abelian groups as | |||
:<math> | |||
\widehat{f}(s) = \sum_{a \in G} f(a) \bar{\chi_s}(a). | |||
</math> | |||
Note that the right-hand side is simply <math>\langle f, \chi_s\rangle</math> for the inner product on the vector space of functions from <math>G\,</math> to <math>\mathbb{C}\,</math> defined by | |||
:<math> | |||
\langle f, g \rangle = \sum_{a \in G} f(a) \bar{g}(a). | |||
</math> | |||
The inverse Fourier transform is then given by | |||
:<math> | |||
f(a) = \frac{1}{|G|} \sum_{s \in G} \widehat{f}(s) \chi_s(a). | |||
</math> | |||
A property that is often useful in probability is that the Fourier transform of the uniform distribution is simply <math>\delta_{a,0},\,</math> where 0 is the group identity and <math>\delta_{i,j}\,</math> is the [[Kronecker delta]]. | |||
==Applications== | |||
This generalization of the discrete Fourier transform is used in [[numerical analysis]]. A [[circulant matrix]] is a matrix where every column is a [[cyclic shift]] of the previous one. Circulant matrices can be [[diagonalization|diagonalized]] quickly using the [[fast Fourier transform]], and this yields a fast method for solving [[system of linear equations|systems of linear equations]] with circulant matrices. Similarly, the Fourier transform on arbitrary groups can be used to give fast algorithms for matrices with other symmetries {{harv|Åhlander|Munthe-Kaas|2005}}. These algorithms can be used for the construction of [[numerical partial differential equations|numerical methods for solving partial differential equations]] that preserve the symmetries of the equations {{harv|Munthe-Kaas|2006}}. | |||
==See also== | |||
*[[Fourier transform]] | |||
*[[Discrete Fourier transform]] | |||
*[[Representation theory of finite groups]] | |||
*[[Character theory]] | |||
==References== | |||
* {{Citation | last1=Åhlander | first1=Krister | last2=Munthe-Kaas | first2=Hans Z. | title=Applications of the generalized Fourier transform in numerical linear algebra | doi=10.1007/s10543-005-0030-3 | mr=2191479 | year=2005 | journal=BIT | volume=45 | issue=4 | pages=819–850}}. | |||
* Diaconis, P. (1988). [http://projecteuclid.org/euclid.lnms/1215467407 ''Group Representations in Probability and Statistics.''] Lecture Notes — Monograph Series, Vol. 11. Hayward, California: Institute of Mathematical Statistics. | |||
* Diaconis, P. (1991). "Finite Fourier Methods: Access to Tools." In ''Probabilistic Combinatorics and its Applications,'' Proceedings of Symposia in Applied Mathematics, Vol. 44. Bollobás, B., and Chung, F. R. K. (ed.). | |||
* {{Citation | last1=Munthe-Kaas | first1=Hans Z. | title=On group Fourier analysis and symmetry preserving discretizations of PDEs | doi=10.1088/0305-4470/39/19/S14 | mr=2220776 | year=2006 | journal=[[Journal of Physics A]] | volume=39 | issue=19 | pages=5563–5584}}. | |||
* Terras, A. (1999). ''Fourier Analysis on Finite Groups and Applications''. Cambridge: Cambridge University Press. | |||
{{DEFAULTSORT:Fourier Transform On Finite Groups}} | |||
[[Category:Fourier analysis]] | |||
[[Category:Finite groups]] |
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In mathematics, the Fourier transform on finite groups is a generalization of the discrete Fourier transform from cyclic to arbitrary finite groups.
Definitions
The Fourier transform of a function at a representation of is
So for each representation of , is a matrix, where is the degree of .
Let be a complete set of inequivalent irreducible representations of . Then, . Then the inverse Fourier transform at an element of is given by
where is the degree of the representation
Properties
Transform of a convolution
The convolution of two functions is defined as
The Fourier transform of a convolution at any representation of is given by
Plancherel formula
For functions , the Plancherel formula states
where are the irreducible representations of
Fourier transform on finite abelian groups
Since the irreducible representations of finite abelian groups are all of degree 1 and hence equal to the irreducible characters of the group, Fourier analysis on finite abelian groups is significantly simplified. For instance, the Fourier transform yields a scalar- and not matrix-valued function.
Furthermore, the irreducible characters of a group may be put in one-to-one correspondence with the elements of the group.
Therefore, we may define the Fourier transform for finite abelian groups as
Note that the right-hand side is simply for the inner product on the vector space of functions from to defined by
The inverse Fourier transform is then given by
A property that is often useful in probability is that the Fourier transform of the uniform distribution is simply where 0 is the group identity and is the Kronecker delta.
Applications
This generalization of the discrete Fourier transform is used in numerical analysis. A circulant matrix is a matrix where every column is a cyclic shift of the previous one. Circulant matrices can be diagonalized quickly using the fast Fourier transform, and this yields a fast method for solving systems of linear equations with circulant matrices. Similarly, the Fourier transform on arbitrary groups can be used to give fast algorithms for matrices with other symmetries Template:Harv. These algorithms can be used for the construction of numerical methods for solving partial differential equations that preserve the symmetries of the equations Template:Harv.
See also
- Fourier transform
- Discrete Fourier transform
- Representation theory of finite groups
- Character theory
References
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- Diaconis, P. (1991). "Finite Fourier Methods: Access to Tools." In Probabilistic Combinatorics and its Applications, Proceedings of Symposia in Applied Mathematics, Vol. 44. Bollobás, B., and Chung, F. R. K. (ed.).
- 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.
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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. - Terras, A. (1999). Fourier Analysis on Finite Groups and Applications. Cambridge: Cambridge University Press.