Hi Noam, I think you want https://urldefense.us/v3/__https://petsc.org/release/manualpages/DMPlex/DMPlexGetClosureIndices/__;!!G_uCfscf7eWS!f8v1_ty7e_mf4QhytGsCFXSd_APEy50GjoLrAL_o294K-EBz1Xa8kEDmeq3UmehbZvBL-u72r4GN6mjxAFf6Ljw$
Indices are ordered globally on the first process (0) first, the proc 1, etc., so the global index is the local index + "my start index". You can get this local start index in a number of ways, eg, https://urldefense.us/v3/__https://petsc.org/main/manualpages/Mat/MatGetOwnershipRange__;!!G_uCfscf7eWS!f8v1_ty7e_mf4QhytGsCFXSd_APEy50GjoLrAL_o294K-EBz1Xa8kEDmeq3UmehbZvBL-u72r4GN6mjxh3g3zew$ if you have a scalar matrix from the DM/section. Thanks, Mark ps, we are at the PETSc annual meeting this week, so may be slow to respond On Mon, May 19, 2025 at 6:58 PM Noam T. via petsc-users < petsc-users@mcs.anl.gov> wrote: > Hello, > > I am trying to build the connectivity matrix for a mesh; i.e. the indices > of the nodes that compose each cell. > > Example: > > 0-------1 > |.\.....| > |...\...| > |.....\.| > 3-------2 > > the matrix would look like [ [0, 3, 2], [2, 1, 0] ] (possibly different > ordering). > > One option is using DMPlexGetTransitiveClosure, and accessing the last > elements in the output "points", which contain the vertex indices. > However, these indices are local per process (both for vertices and > cells). Is it possible to get the global indices? > > I tried a mapping, as in example 14f ( > https://urldefense.us/v3/__https://petsc.org/release/src/ksp/ksp/tutorials/ex14f.F90.html__;!!G_uCfscf7eWS!f8v1_ty7e_mf4QhytGsCFXSd_APEy50GjoLrAL_o294K-EBz1Xa8kEDmeq3UmehbZvBL-u72r4GN6mjxUrZKlTM$ > > <https://urldefense.us/v3/__https://petsc.org/release/src/ksp/ksp/tutorials/ex14f.F90.html__;!!G_uCfscf7eWS!ezMKlDED-8WxXpg_Elxus7WhYkZzCA5OmmLe6vHZGFoj4se5S5RD5ZgTrC3TYErx8znYKebSW-s0H0mt1_MEMAzpmFDwr0PH$> > ) > > --- > DM :: dm > ISLocalToGlobalMapping :: ltog_map > PetscInt, pointer :: ltog_idx(:) > > ! ... > ! Create a dm from a mesh file > ! ... > DMGetLocalToGlobalMapping(dm,ltog_map,ierr) > ISLocalToGlobalMappingGetIndices(ltog_map, ltog_idx, ierr) > --- > > but the returned array ltog is empty (ISLocalToGlobalMappingGetSize() > returns zero). Are there other functions calls needed before being able > to create this mapping? Or is this mapping simply not usable in this case? > > Is there perhaps better/simpler way to get this connectivity? > > Thank you. > Noam > >
