t=-3:0.125:3;
x=sin(2.*t);y=cos(2.*t);[x,y]=meshgrid(x,y);
z=x.^2+2*y.^2;
mesh(x,y,z)
axis([-1 - -1 - 0 3])
pause
meshc(x,y,Z)
pause
surf(x,y,z)