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Question

Math 6410 • ODE

Fall 2008 • Question 10

  1. Solve Poisson’s equation \[ \nabla ^2u=f\text { in }D,\qquad u=g\text { on }\partial D \] in terms of an appropriately defined Green’s function.
  2. Show that the two–dimensional Green’s function for the Laplacian in an unbounded domain is \[ G(\mathbf {x},\mathbf {x}')=\frac {1}{2\pi }\ln \lvert \mathbf {x}-\mathbf {x}'\rvert . \]
  3. Use the method of images to derive the Green’s function for the Laplacian in the half–space \(x\in \mathbb {R}\), \(y>0\) with a Dirichlet boundary condition on \(y=0\), and evaluate the corresponding solution of part (a) when \(f=0\).

Raw LaTeX

\begin{enumerate}
\item[(a)] Solve Poisson's equation
\[
  \nabla^2u=f\text{ in }D,\qquad u=g\text{ on }\partial D
\]
in terms of an appropriately defined Green's function.

\item[(b)] Show that the two--dimensional Green's function for the Laplacian in an
unbounded domain is
\[
  G(\mathbf{x},\mathbf{x}')=\frac{1}{2\pi}\ln\lvert\mathbf{x}-\mathbf{x}'\rvert.
\]

\item[(c)] Use the method of images to derive the Green's function for the Laplacian
in the half--space \(x\in\R\), \(y>0\) with a Dirichlet boundary condition on \(y=0\),
and evaluate the corresponding solution of part (a) when \(f=0\).
\end{enumerate}