How to plot a variable against two other dependent variables

Suppose I have a variable z = f(x,y). How can I generate a 2D plot with z along the vertical axis with x along the bottom horizontal axis and y along the top horizontal axis? Or I could have two bottom axis, one for x and one for y.

[Azzi Abdelmalek]

I don't think it's possible, a 2D plot require only 2 values

Answer 1

[Sean de Wolski]

[xx yy] = meshgrid(x,y);
Z = f(xx,yy);

mesh(xx,yy,Z)

or

surf(xx,yy,Z);