clear all; close all;
grid = 0.1:0.05:2;
[X Y] = meshgrid(grid,grid);
R = sqrt(X.^2+Y.^2);
f = 1/pi*1/sqrt(2*pi)*1./R.*exp(-1/2*R.^2);
contour(X,Y,f,20);
axis equal;
xlim([grid(1) grid(end)]);
ylim([grid(1) grid(end)]);