Basically I have two curves, P1 and P2, which are dependent on Q1 and Q2 in a square manner. For example, P1:=1+Q1^2 and P2:=5-Q2^2. I now want to plot P1 and P2 on the same graph with the values of P1 and P2 on the same z-axis and Q1 and Q2 along the x- and y-axes. Consequently I would get two orthogonal parabolic curves. plot3d([P1,P2],Q1=-1..1,Q2=-1..1) doesn't work because it obviously draws two surfaces rather than two curves for P1 with Q2 always equal to zero and vice versa P2 with Q1 always equal to zero.