Jed Brown writes: > On Tue, Nov 29, 2011 at 23:53, Dave Nystrom <dnystrom1 at comcast.net> wrote: > > > I have a resistive mhd code that I have recently interfaced to petsc which > > has 7 linear solves that are all symmetric. I recently tried using > > -pc_type > > cholesky -ksp_type preonly for a run and found that it was taking about 6 > > times as long per linear solve as when I was using -pc_type lu -ksp_type > > preonly. > > > > Try -pc_factor_mat_ordering_type nd > > > > I was wondering if that was reasonable behavior. I would not have > > thought that using a cholesky direct solve would take longer than an LU > > direct solve in petsc for the serial case and was hoping it would be > > faster. > > Does this behavior seem reasonable? > > > > Try this: > > -pc_type cholesky -pc_factor_mat_ordering_type nd
Thanks. I'll give this a try and report back on the results. > Barry, why is natural ordering still the default for Cholesky? It is so > slow that it is worthless.