On Sun, Jul 23, 2023 at 11:54 AM 袁煕 <yua...@advancesoft.jp> wrote:
> 袁煕 <yua...@advancesoft.jp> > 0:50 (0 分前) > To PETSc > Hi, > > I used PETSc to assemble a FEM stiff matrix of an overlapped (overlap=2) > DMPlex and used the MUMPS solver to solve it. But I got a > different solution by using 1 CPU and MPI parallel computation. I am > wondering if I missed some necessary step or setting during my > implementation. > > My calling process like follows > > 1. Generate matrix pkij from DMPlex dm_mesh > > ``` > PetscCallA( DMCreateMatrix(dm_mesh, pkij, ierr) ) > PetscCallA( MatSetBlockSize(pkij, 1, ierr)) > if( overlap>0 ) call > MatSetOption(pkij,MAT_IGNORE_OFF_PROC_ENTRIES,PETSC_TRUE,ierr) > PetscCallA( MatSetFromOptions(pkij, ierr)) > > PetscCallA(MatGetLocalSize(pkij, m, n, ierr)); > PetscCallA(MatGetSize(pkij, gm, gn, ierr)); > PetscCallA(MatGetBlockSize(pkij, bs, ierr)); > ``` > > 2. Do Matrix preallocation > > ``` > PetscCallA(MatCreate(PETSC_COMM_WORLD, preallocator, ierr)); > PetscCallA(MatSetType(preallocator, MATPREALLOCATOR, ierr)); > PetscCallA(MatSetSizes(preallocator, m, n, gm, gn, ierr)); > PetscCallA(MatSetBlockSize(preallocator, bs, ierr)); > PetscCallA(MatSetUp(preallocator, ierr)); > > ....... > > PetscCallA( MatPreallocatorPreallocate(preallocator, PETSC_TRUE, pkij, > ierr) ) > PetscCallA( MatDestroy(preallocator,ierr) ) > ``` > > 3. Assemble matrix pkij by calling MatSetValue of all overlapped elements. > > In my above implementation, I used > MatSetOption(pkij,MAT_IGNORE_OFF_PROC_ENTRIES,PETSC_TRUE,ierr). Is that > correct? Or even other options are needed? > > Do you want to ignore off-process entries? Usually in FEM we share part of the boundary with other processes, and thus ignoring the off-process entries will not give the correct result. Thanks, Matt > > > Thanks for your help. > > ------ > > X. Yuan, Ph.D. of solid mechanics > > Advancesoft, Japan > > --------- > > -- 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/>