x=linspace(-2*pi,2*pi,21);
y=linspace(-1.5*pi,1.5*pi,31);
[xx,yy]=meshgrid(x,y);
zz=sin(xx/2).*cos(yy);
subplot(1,2,1)
surf(xx,yy,zz);axis image;
subplot(1,2,2)
contour(xx,yy,zz);axis image;