Matlab for Unwrapping Spectral Phase

When spectral phase is processed, it is often necessary to unwrap the phase to make it a ``continuous'' function. Below is a simple matlab function for this purpose. It is based on the assumption that phase jumps by more than $\pi$ radians must have been ``wrapped''. That is, multiples of $2\pi$ are added or subtracted so that the phase changes by no more than $\pm\pi$ from one spectral bin to the next. Bin 0 (corresponding to dc) is arbitrarily chosen as ``unwrapped'' and used as a starting point for the unwrapping algorithm.