subplot(2,2,2);
x=-pi/2:pi/10:pi/2;
y=sqrt(cos(x));
plot(x,y);
subplot(2,2,3);
x=-2:0.1:2;
y=-4:0.1:4;
[x,y]=meshgrid(x,y);
z=x.^2/4+y.^2/16;
surf(x,y,z)