On Thu, Oct 11, 2018 at 3:26 PM Michael Wick <michael.wick.1...@gmail.com> wrote:
> Thanks for all the suggestions! > > Increasing the value of icntl_14 in MUMPS helps a lot for my case. > > Do you have any suggestions for higher-order methods in saddle-point > problems? > It depends on what the Schur complement looks like. Matt > Mike > > Dave May <dave.mayhe...@gmail.com> 于2018年10月11日周四 上午1:50写道: > >> >> >> On Sat, 6 Oct 2018 at 12:42, Matthew Knepley <knep...@gmail.com> wrote: >> >>> On Fri, Oct 5, 2018 at 9:08 PM Mike Wick <michael.wick.1...@gmail.com> >>> wrote: >>> >>>> Hello PETSc team: >>>> >>>> I am trying to solve a PDE problem with high-order finite elements. The >>>> matrix is getting denser and my experience is that MUMPS just outperforms >>>> iterative solvers. >>>> >>> >>> If the problem is elliptic, there is a lot of evidence that the P1 >>> preconditioner is descent for the system. Some people >>> just project the system to P1, invert that with multigrid, and use that >>> as the PC for Krylov. It should be worth trying. >>> >> >> Matt means project to P1 directly from your high order function space in >> one step. It is definitely worth trying. >> For those interested, this approach is first described and discussed (to >> my knowledge) in this paper: >> >> Persson, Per-Olof, and Jaime Peraire. "An efficient low memory implicit >> DG algorithm for time dependent problems." *44th AIAA Aerospace Sciences >> Meeting and Exhibit*. 2006. >> >> >>> Moreover, as Jed will tell you, forming matrices for higher order is >>> counterproductive. You should apply those matrix-free. >>> >> >> I definitely agree with that. >> >> Cheers, >> Dave >> >> >> >>> >>> Thanks, >>> >>> Matt >>> >>> >>>> For certain problems, MUMPS just fail in the middle for no clear >>>> reason. I just wander if there is any suggestion to improve the robustness >>>> of MUMPS? Or in general, any suggestion for interative solver with very >>>> high-order finite elements? >>>> >>>> Thanks! >>>> >>>> Mike >>>> >>> >>> >>> -- >>> What most experimenters take for granted before they begin their >>> experiments is infinitely more interesting than any results to which their >>> experiments lead. >>> -- Norbert Wiener >>> >>> https://www.cse.buffalo.edu/~knepley/ >>> <http://www.cse.buffalo.edu/~knepley/> >>> >> -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>