Hi Alexander, I am just curious how other sparse direct solver (eg. PaStiX) works on your problem. Right now, I only have single RHS, but I will need multi-RHS soon. For my single RHS problem, PaStiX works better for my sparse matrix pattern (helmholtz like). If you tried PaStiX, I would be happy to know the comparison between these solvers. Thanks.
Xiangdong On Mon, Dec 12, 2011 at 10:22 AM, Alexander Grayver <agrayver at gfz-potsdam.de> wrote: > Matt, Barry & Hong, > > Thanks a lot for response. > I may be wrong, but I think that people chose direct solvers for their > robustness and ability to solve for many RHS very quickly. > Surely I don't expect my solution to be sparse and it is not, but at least > in electromagnetics it is pretty common to have sparse RHS. > I am wondering how about other disciplines? > > I don't know about other solvers, but when I use multiple RHS in mumps it > works several times faster then solving for them sequentially. It is just my > experience. > > And I also can imagine that using sparsity is another obvious advantage if > you have sparse RHS. > Now for 1000 rhs and a system of order 10^6 I need 32 gb to use MatMatSolve > with double complex arithmetic. For instance, LDLt factorization of matrix > 10^6 takes ~80 gb. > One option would be to use MatMatSolve(A,X,X) thus reducing memory > consumption twice. > > >>> ?I doubt it is feasible for thousands of rhs. > > > You're right, it is not. It is feasible only if you have sparse RHS. > > Regards, > Alexander > > > On 12.12.2011 15:37, Hong Zhang wrote: >> >> Reading MUMPS manual, mumps only supports centralized dense and sparse >> rhs, >> while solution can be centralized or distributed, but only in the >> dense format (because manual >> does not mention sparse solu). >> >> It would be easy to add MatMatSolve() in Petsc-mumps interface for dense >> rhs, >> but will require vecscatter of petsc distributed dense matrix for rhs >> to mumps centralized >> dense rhs - I doubt it is feasible for thousands of rhs. >> >> Hong >> >> >> On Mon, Dec 12, 2011 at 8:26 AM, Barry Smith<bsmith at mcs.anl.gov> ?wrote: >>> >>> ? Alexander, >>> >>> ? ?Do you expect that solving with a sparse right hand side will result >>> in an answer that is also sparse? Normally once you've done the lower >>> triangular solve and then the upper triangular solve won't the result be >>> dense? >>> >>> ? ?Barry >>> >>> On Dec 12, 2011, at 3:10 AM, Alexander Grayver wrote: >>> >>>> Hi Barry, >>>> >>>> Thanks for answer. I should have asked about that from the very >>>> beginning actually. >>>> I get 2 times decrease in performance with 20 RHS, I can imagine how >>>> slow it will be when I will use thousands of them, >>>> moreover it will require a lot of memory to store them as a dense >>>> matrix. >>>> >>>> On 11.12.2011 18:50, Barry Smith wrote: >>>>> >>>>> On Dec 11, 2011, at 9:29 AM, Alexander Grayver wrote: >>>>> ? ?One by one >>>> >>>> I'm wondering why? All main direct packages like MUMPS, SuperLU_DIST, >>>> PaSTiX support multiple RHS. >>>> >>>>> ? ?We do not handle a sparse right hand side. >>>> >>>> Since I already transferred my code to PETSc anyway, my question now if >>>> it's possible to implement sparse multiple RHS and solve them >>>> simultaneously? >>>> Something like MatMatSolveSparse. I would implement it myself, the >>>> question is there a way to integrate it into PETSc as a patch or something >>>> like that? >>>> >>>> Regards, >>>> Alexander > >
