permutation to block triangular form library for sparse matrices

 Suitesparse is a collection of libraries for computations involving
 sparse matrices.
 .
 The BTF library is a software package for permuting a matrix into Block upper
 Triangular Form. It includes a maximum transversal algorithm, which finds a
 permutation of a square or rectangular matrix so that it has a zero-free
 diagonal (if one exists); otherwise, it finds a maximal matching which
 maximizes the number of nonzeros on the diagonal. The package also includes a
 method for finding the strongly connected components of a graph. These two
 methods together give the permutation to block upper triangular form.