2D Poisson equation. Multigrid. Fixed boundaries

This GPU based script draws ui,n/2 cross-section after one multigrid V-cycle with the reduction level = 5 and "deep" relaxation iterations 2rel. Boundaries are fixed
fi,j = sin(πi/n) sin(πj/n)
n rel level ω
To get fixed boundaries on k×k texture (with periodic boundaries) we render (-1 + 2/k, -1 + 2/k,   1, -1 + 2/k,   -1 + 2/k, 1,   1, 1) square (see the page source for detaile).
Simulations on GPU     updated 25 July 2012