> Am 24.07.2021 um 07:32 schrieb Barry Smith <bsm...@petsc.dev>: > > > Qi, > > MatSetLocalGlobalToGlobalMapping() is the routine that provides the > information to the matrix so that one can use a "local" ordering and it will > get automatically translated to the parallel PETSc ordering on the parallel > matrix. Generically yes it includes the ghost point region on each MPI rank. > Some DM's provide this information automatically; for DMDA it is pretty > simple, for DMStag a bit more complicated. > The local-to-global mapping should get automatically attached to the Mat if you use a DM to create an operator/Mat, with DMCreateMatrix(). Thus, this is the recommended way to proceed!
https://petsc.org/release/docs/manualpages/DM/DMCreateMatrix.html > You are correct, the previous manual page for MatZeroRowsLocal() > incorrectly states "global" rows from 16+ years ago, likely a cut and paste > error. It looks like it has been fixed in the main PETSc repository, > > Barry > > >> On Jul 23, 2021, at 10:50 AM, Tang, Qi <tan...@msu.edu >> <mailto:tan...@msu.edu>> wrote: >> >> How can we use MatZeroRowsLocal? Is there any doc for the local index vs >> global index for a matrix? >> >> I am asking because we are not sure about how to prepare a proper local >> index. Does the index include the ghost point region or not? >> >> Qi >> >> >> >> >>> On Jul 20, 2021, at 9:30 PM, Tang, Qi <tan...@msu.edu >>> <mailto:tan...@msu.edu>> wrote: >>> >>> Hi, >>> >>> Now I think the DMStagStencilToIndexLocal provides the local index for >>> given (stencil) positions. How can we use that local index information to >>> eliminate the rows? >>> >>> Is the following code possible: >>> >>> MatSetLocalToGlobalMapping(…); >>> If (is_boundary){ >>> PetscInt ix; >>> DMStagStencilToIndexLocal(…, &ix); >>> MatZeroRowsLocal(… &ix, …); >>> } >>> >>> The comment of MatZeroRowsLocal said "rows - the global row indices”. But >>> this seems inconsistent with its name, so I am confused. >>> >>> Thanks, >>> Qi >>> >>> >>>> On Jul 20, 2021, at 2:18 AM, Patrick Sanan <patrick.sa...@gmail.com >>>> <mailto:patrick.sa...@gmail.com>> wrote: >>>> >>>> Hi Qi - >>>> >>>> I just opened a PR to make DMStagStencilToIndexLocal() public >>>> https://gitlab.com/petsc/petsc/-/merge_requests/4180 >>>> <https://urldefense.com/v3/__https://gitlab.com/petsc/petsc/-/merge_requests/4180__;!!HXCxUKc!mAeQntyQFk-B3KHmJJWuOGKXTfKh8A-uC-v9JFZHW-VbJT7ejxWH7LlaFNM-Zg$> >>>> >>>> (Sorry for my inattention - I think I may have missed some communications >>>> in processing the flood of PETSc emails too quickly - I still plan to get >>>> some more automatic DMStag fieldsplit capabilities into main, if it's not >>>> too late). >>>> >>>>> Am 20.07.2021 um 02:47 schrieb Tang, Qi <tan...@msu.edu >>>>> <mailto:tan...@msu.edu>>: >>>>> >>>>> Hi, >>>>> As a part of implementing this process by ourself, we would like to >>>>> eliminate boundary dofs. By reading DMStag code, we guess we can use >>>>> DMStagStencilToIndexLocal >>>>> MatZeroRowsLocal >>>>> >>>>> We note that DMStagStencilToIndexLocal is not explicitly defined in the >>>>> header file. Is this function ready to use? And will we be able to >>>>> eliminate the dofs using the above functions? >>>>> >>>>> Thanks, >>>>> Qi >>>>> >>>>> >>>>> >>>>>> On Jul 16, 2021, at 8:17 PM, Barry Smith <bsm...@petsc.dev >>>>>> <mailto:bsm...@petsc.dev>> wrote: >>>>>> >>>>>> >>>>>> Zakariae, >>>>>> >>>>>> MatGetSubMatrix() was removed a long time ago, the routine is now >>>>>> MatCreateSubMatrix() but it does not work in way you had hoped. There is >>>>>> currently no mechanism to move values you put into the sub matrix back >>>>>> into the original larger matrix (though perhaps there should be?). >>>>>> >>>>>> Please look at MatCreateSubMatrixVirtual() and also MatCreateNest() >>>>>> to see if either of those approaches satisfy your needs. >>>>>> >>>>>> Please let us know if there are extensions that would be useful for >>>>>> you to accomplish what you need. >>>>>> >>>>>> Barry >>>>>> >>>>>> >>>>>>> On Jul 16, 2021, at 7:45 PM, Jorti, Zakariae via petsc-users >>>>>>> <petsc-users@mcs.anl.gov <mailto:petsc-users@mcs.anl.gov>> wrote: >>>>>>> >>>>>>> Hello, >>>>>>> >>>>>>> I have a matrix A = [A00 , A01 ; A10, A11]. >>>>>>> I extract the submatrix A11 with MatGetSubMatrix. >>>>>>> I only know the global IS is1 and is2, so to get A11 I call: >>>>>>> MatGetSubMatrix(A,is2,is2,MAT_INITIAL_MATRIX,&A11); >>>>>>> I want to modify A11 and update the changes on the global matrix A but >>>>>>> I could not find any MatRestoreSubMatrix routine. >>>>>>> Is there something similar to VecGetSubVector and VecRestoreSubVector >>>>>>> for matrices that uses only global indices? >>>>>>> Many thanks. >>>>>>> Best regards, >>>>>>> >>>>>>> Zakariae >>>>>> >>>>> >>>> >>> >> >
