# Math Help - PDE

1. ## PDE

Hello!

How can I find out the max and min of u(x,y)?
I don't know how to use the maximum principle in this case.

Thank you!

2. ## Re: PDE

Hi

In the case of your problem ($\Delta u=0$ and $\Omega$ bounded), the (weak) principle maximum says that the function $u$ reaches his maximum (resp. his minimum) on the boundary of the domain $\Omega$. So the maximum and the minimum of the solution $u$ of your problem is relatively simple to find.