Matrix logarithm

Two functions for computing the matrix logarithm by the inverse scaling and squaring method.

This submission contains two functions for computing the matrix
logarithm by the inverse scaling and squaring method. LOGM_NEW uses a
Schur decomposition, while LOGM_ISS_FULL is transformation-free and
works entirely with the original matrix. Both incorporate several
improvements over previous algorithms.

Function TEST.M runs a simple test of the codes.

Details on the underlying algorithms can be found in

A. H. Al-Mohy and N. J. Higham. Improved Inverse Scaling and Squaring
Algorithms for the Matrix Logarithm. MIMS EPrint 2011.83, The University
of Manchester, October 2011. http://eprints.ma.man.ac.uk/1687