trying a simple one x[1]:.5; x[2]:sqrt(1-x[1]^2) * cos(2*t); x[3]:sqrt(1-x[1]^2) * sin(2*t); plot3d([x[1],x[2],x[3]], [t,0,2*%pi],[s,0,1]); causes a zero divide, which I don't understand, since I am not dividing anything. thanks