Underwater acoustics

Navigation function usually refers to a function of position, velocity, acceleration and time which is used to plan robot trajectories through the environment. Generally, the goal of a navigation function is to create feasible, safe paths that avoid obstacles while allowing a robot to move from its starting configuration to its goal configuration.

Potential functions as navigation functions

File:Pf as navigation function.png

A potential function. Imagine dropping a marble on the surface. It will avoid the three obstacles and eventually reach the goal position in the center.

Potential functions assume that the environment or work space is known. Obstacles are assigned a high potential value, and the goal position is assigned a low potential. To reach the goal position, a robot only needs to follow the negative gradient of the surface.

We can formalize this concept mathematically as following: Let $X$ be the state space of all possible configurations of a robot. Let $X_g\subset X$ denote the goal region of the state space.

Then a potential function $\varphi (x)$ is called a (feasible) navigation function if

1. $\varphi (x)=0\mathrm{\forall }x\in X_g$
2. $\varphi (x)=\mathrm{\infty }$ if and only if no point in $X_G$ is reachable from $x$.
3. For every reachable state, $x\in X\setminus X_G$, the local operator produces a state $x^{\prime }$ for which $\varphi (x^{\prime })<\varphi (x)$.

Navigation Function in Optimal Control

While for certain applications, it suffices to have a feasible navigation function, in many cases it is desirable to have an optimal navigation function with respect to a given cost functional $J$. Formalized as an optimal control problem, we can write

$\text{minimize }J(x_{1:T},u_{1:T})=\underset{T}{\int }L(x_t,u_t,t)dt$

$\text{subject to }\dot{x_t}=f(x_t,u_t)$

whereby $x$ is the state, $u$ is the control to apply, $L$ is a cost at a certain state $x$ if we apply a control $u$, and $f$ models the transition dynamics of the system.

Applying Bellman's principle of optimality the optimal cost-to-go function is defined as

$\varphi (x_t)={\min }_{u_t\in U(x_t)}\{L(x_t,u_t)+\varphi (f(x_t,u_t))\}$

Together with the above defined axioms we can define the optimal navigation function as

1. $\varphi (x)=0\mathrm{\forall }x\in X_g$
2. $\varphi (x)=\mathrm{\infty }$ if and only if no point in $X_G$ is reachable from $x$.
3. For every reachable state, $x\in X\setminus X_G$, the local operator produces a state $x^{\prime }$ for which $\varphi (x^{\prime })<\varphi (x)$.
4. $\varphi (x_t)={\min }_{u_t\in U(x_t)}\{L(x_t,u_t)+\varphi (f(x_t,u_t))\}$

Stochastic Navigation Function

If we assume the transition dynamics of the system or the cost function as subjected to noise, we obtain a stochastic optimal control problem with a cost $J(x_t,u_t)$ and dynamics $f$. In the field of reinforcement learning the cost is replaced by a reward function $R(x_t,u_t)$ and the dynamics by the transition probabilities $P(x_{t+1}|x_t,u_t)$.

See also

• Control Theory
• Optimal Control
• Robot Control
• Motion Planning
• Reinforcement Learning

References

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• 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
  
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  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

External links

• NFsim: MATLAB Toolbox for motion planning using Navigation Functions.

References

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