How can I draw equipotential surface?

For example, we have a function

f(x,y,z) = (x * y) * exp(-r)/r

with r = sqrt(x^2+y^2+z^2).

Then I want to draw the equipotential surface of this function,

the surface that satisfies f(x,y,z) = 1 or f(x,y,z) = 0.5... and something else.

How can I do it?

Answer 1

[Mike Garrity]

This post I wrote for the MATLAB Graphics blog explains the basic idea behind drawing implicit surfaces like this.