Green's function in elliptic box

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Discussion Overview

The discussion centers on finding an expression for the Green's function for Poisson's equation that vanishes on an ellipse in two dimensions. Participants explore potential methods and references related to the construction of this Green's function, particularly in relation to elliptical coordinates and existing solutions for circular geometries.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the existence of a Green's function for Poisson's equation that vanishes on an ellipse, noting the known solution for a circle.
  • Another participant suggests that Laplace's equation on an ellipse is separable in elliptical coordinates and can be expressed using Mathieu functions, which may aid in constructing the Green's function.
  • A different participant expresses concern that solving Laplace's equation may not be applicable since the Laplacian of the Green's function equals the Dirac delta, not zero, and questions whether the same technique is valid.
  • One participant argues that the Green's function equation resembles Laplace's equation except at a singular point, implying that solutions to Laplace's equation could be used to derive the Green's function, while also acknowledging the potential for various methods involving elliptical coordinates and Mathieu functions.
  • Another participant expresses intent to search for more information based on the suggestions provided.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best approach to derive the Green's function for the elliptical case, with multiple competing views on the applicability of techniques and the relevance of existing solutions.

Contextual Notes

Participants mention the need for references and the complexity of the algebra involved in constructing the Green's function, indicating that the discussion may depend on specific mathematical techniques and definitions related to elliptical coordinates and Mathieu functions.

Einj
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Hello everyone! Does anyone know if there is a know expression for the Green's function for Poisson's equation that vanishes on an ellipse in 2 dimensions?
I'm essentially looking for a solution to:
$$
\nabla^2G(\vec x-\vec x_0)=\delta^2(\vec x-\vec x_0)
$$
in 2 dimensions where
$$G(\vec x-\vec x_0)=0$$
when \vec x lies on an ellipse.
The solution for a circle is well know but I wanted to know if there any kind of generalization.

Thanks a lot!
 
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If I remember correctly Laplace's equation on an ellipse is separable if you use elliptical coordinates, and the solution can be expressed in terms of Mathieu functions. From this one should be able to construct the Green's function.
 
Well, I don't really want to solve Laplace equation since the Laplacian of the Green's function is not equal to zero but to the Dirac delta. Do you think the same technique still holds? Do you have any reference?
 
If you think about it the Green's function equation is equal to Laplace's equation everywhere except for at one point. You can use the solution to Laplace's equation to construct the Green's function. It takes a little bit of algebra, but it is tractable. Of course there are other ways to solve for the Green's function. I bet most of them will probably use elliptical coordinates and Mathieu funtions.

I don't have references on hand, but Googling elliptical greens function produces some promising hits.
 
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Ok I will definitely do that! Thanks a lot.
 

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