Laplace equation and Median Value Property

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SUMMARY

The discussion centers on solving the Laplace equation $u_{xx}+u_{yy}=0$ within the unit disk defined by $\{(x,y)\in \mathbb{R}^2: x^2+y^2<1\}$. The boundary condition is given as $u(x,y)=x$ for points on the unit circle where $x^2+y^2=1$. Utilizing the Median Value Property, the value of $u$ at the origin $(0,0)$ can be determined as $u(0,0) = 0$. This conclusion is derived from the property that the value of a harmonic function at a point is the average of its values over any circle centered at that point.

PREREQUISITES
  • Understanding of the Laplace equation and harmonic functions.
  • Familiarity with the Median Value Property in potential theory.
  • Basic knowledge of calculus and multivariable functions.
  • Concepts of boundary conditions in partial differential equations.
NEXT STEPS
  • Study the properties of harmonic functions in detail.
  • Explore the derivation and applications of the Median Value Property.
  • Learn about boundary value problems in the context of partial differential equations.
  • Investigate numerical methods for solving Laplace's equation in various domains.
USEFUL FOR

Mathematicians, physicists, and engineering students interested in partial differential equations, particularly those studying harmonic functions and their properties.

Julio1
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Suppose that $u$ is the solution of the Laplace equation

$u_{xx}+u_{yy}=0$ in $\{(x,y)\in \mathbb{R}^2: x^2+y^2<1\}$

$u(x,y)=x$ for all $(x,y)\in \mathbb{R}^2$ such that $x^2+y^2=1.$

Find the value of $u$ in $(0,0).$ Use the property of median value.
Hello. The median value is $u(x)=\dfrac{\displaystyle\int_{\partial B(x,r)} u(y)dS(y)}{\displaystyle\int_{\partial B(x,r)} \, dS(y)}$. But how can apply for this case?
 
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Hello :). I don't can solve this... Can any help me?
 

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