# Existence of a function

[also asked here http://math.stackexchange.com/questions/307197]

All arguments are in $\mathbb{R}^3$.

Suppose $n(x)$ is a smooth function where $\mathbf{supp}(n(x)-1)$ is a compact set $\Omega$. i.e. $n(x) = 1$ when $x$ is outside $\Omega$.

Assume there are some points $x_j\in\Omega$, where $j=1,2,\cdots.m$.

Consider Helmholtz equation

$\Delta u + k^2 n(x) u = 0$

And I want to know if there is a function $u$ satisfies the equation and also vanishes at $x_j$. i.e. $u(x_j) = 0$. [Certainly $u$ can have a manifold of zeros, here I just restrict it on $x_j$]

Here you may try to give a method to construct $u$, or prove the existence.

And you may take $m=1$ here at first.

Thanks.

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This was crossposted to math.SE: math.stackexchange.com/questions/307197 . In the future, please wait some time before posting your question in multiple fora, and when you do, provide links to the other posts - as you can imagine, it would be frustrating for someone to put time into answering your question here, only to see hear from you that you'd already gotten the solution elsewhere. – Zev Chonoles Feb 18 '13 at 16:26
ok, I will put the link here. – Yimin Feb 18 '13 at 16:28

## 1 Answer

I proved the existence here.

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