Computes the inverse of a matrix that has been decomposed into `u,' `w' and `v' by singular value decomposition. It assumes the ``small'' elements of `w' have already been zeroed. It computes the inverse by constructing a diagonal matrix `w2' from `w' (which is just a vector of the diagonal elements, and then explicitly multiplying u^t w2 and v. Note that if you are computing the inverse merely to solve one or more systems of equations, you are better off using the decomposition and backsubstitution routines directly.