Black Hole

x=linspace(0,2*%pi,nn);
t=linspace(0,1,20);
cosphi=dup(cos(x),length(t));
sinphi=dup(sin(x),length(t));
f=dup((t.*t+0.2)',length(x));
plot3d2(f.*cosphi,f.*sinphi,dup(t'.*2-1,length(x)));