Add MUMPS

[garth-wells]

Adding MUMPS would provide a parallel direct solver.

MUMPS is packaged at https://github.com/conda-forge/mumps-feedstock, but will probably need some work. The MUMPS conda package depends on scotch rather than pt-scotch, which may mean that it won't work in parallel.

There is also an issue with scalpack to sort out.

[dalcinl]

OK, then here goes my proposal: If the mumps package is not built with MPI as we need, then we create our own mumps-mpi package, make it use pt-scotch (and create that package as well if required), and also parmetis, and I guess the issue with scalapack is that there is no package yet, right? so have another one to create... All of them should be built for both MPICH and Open MPI. Yes, this is quite a bit of work, but it will pay off in the long run.

[garth-wells]

I would forget ParMETIS (for the time being, and maybe forever). It is not available under an open source license (see http://glaros.dtc.umn.edu/gkhome/metis/parmetis/download).

pt-scotch is available on conda-forge (as a branch under the scotch feedstock, https://github.com/conda-forge/scotch-feedstock/tree/ptscotch).

[minrk]

I started scalapack here, and asked about where folks would like to put parallel mumps here.