[x,y,z]=meshgrid(-3:.1:3, -3:.1:3, -3:.1:3);
f=x.^4-5*x.^2+y.^4-5*y.^2+z.^4-5*z.^2+11.8;
const=0;
surfcv(x,y,z,f,const)
shading interp
axis off
colormap(hot)
light