i.e., a 3d plot, one plane above the other, the bottom one x,i and the top one f(x,i) and a line from each x,i originating from one plane ending at the plane above.
You'd have to skip some values and have some amount of transparency ... but I think it might be interesting to see how the values map from one domain into the other.
Does something like this already exist?
You can plot magnitude and phase as a colored surface, as you probably know.
What is this, an equation for ants?