  The usefulness of Gabor frames depends on the easy computability of a
suitable dual window. This question is addressed under several aspects: several
versions of Schulz's iterative algorithm for the approximation of the canonical
dual window are analyzed for their numerical stability. For Gabor frames with
totally positive windows or with exponential B-splines a direct algorithm
yields a family of exact dual windows with compact support. It is shown that
these dual windows converge exponentially fast to the canonical dual window.
