Torus

x=linspace(0,2*%pi,40);
y=linspace(0,2*%pi,20)';
factor=1.5+cos(y)*(cos(x)/2+0.6);
X=factor*diag(cos(x));
Y=factor*diag(sin(x));
Z=sin(y)*(cos(x)/2+0.6);
plot3d2(X,Y,Z);