Cleanup permutations

[jgdumas]

blackbox/permutation.h
matrix/ BlasPermutation & MatrixPermutation

Is MatrixPermutation then same as blackbox/permutation.h ?

[bdsaunders]

The answer is yes, MatrixPermutation from matrix/matrix-permutation.h and Permutation from blackbox/permutation.h make the same representation. Meanwhile BlasPermutation is the Lapack style rep used in fflas/ffpack.

Five points:

1. I don't see a need for two representations of permutations.
2. I currently have an interest in providing a weighted permutation blackbox.
3. I want to wrap fflas factorizations in the FIBBs (fast inverse blackbox) framework including the permutations,
4. It seems to me that permutations belong in blackbox/, reserving matrix/ for sparse and dense representations.
5. I'm not too happy with the BlasPermutation name (what is it to do with blas?). Perhaps LapackPermutation or simply Permutation can be the name?

I propose to do the following; please comment.

1. Evolve the current blackbox/permutation.h to a weighted-permutation.h using that representation (having an array P where the permutation sends i to P[i] ). (In part this is a compromise to not throw away this representation altogether.)

2. Move matrix/matrix-permutation.h to blackbox/permutation.h, holding the lapack style representation and wrapping the fflas/pack perms.

[jgdumas]

Sounds good to me !