[math-fun] moore-penrose inverse

I've been playing with the q-derivative operator Df = (f(qx)-f(x))/(qx-x) over a finite field. It's obviously singular, since adding a constant to f makes no difference to the derivative. Given a matrix rep for D, I can use Gauss-Jordan elimination to find a matrix rep for an integral operator S such that DSf = f iff there exists some F such that DF = f. I'd like to have an algebraic rep for S like the formula for the q-derivative, but I have no idea how to go about it. Can anyone help? Thanks, -- Mike Stay staym@clear.net.nz http://www.cs.auckland.ac.nz/~msta039