[X,Y] = meshgrid([-1:.05:1]);
Z = (min(0, X + Y)).^2 - 2*X.*Y;
%[c, h] =  contour3(X, Y, Z, 30);
%h2 =  surface(X,Y,Z,'EdgeColor', [.8 .8 .8], 'FaceColor', 'none')
% grid off
%view([142.5, 30])
[c,h] = contour(X, Y, Z);
clabel(c,h); 
%colorbar;
