1#include <petsc/finclude/petsc.h> 2program ex14f90 3 use petsc 4 implicit none 5 6 type(tDM) :: dm 7 type(tVec) :: u 8 type(tPetscSection) :: section 9 PetscInt :: dim, numFields, numBC 10 PetscMPIInt :: rank 11 PetscInt, dimension(2) :: numComp 12 PetscInt, dimension(12) :: numDof 13 PetscInt, dimension(:), pointer :: remoteOffsets 14 type(tPetscSF) :: pointSF 15 type(tPetscSF) :: sectionSF 16 PetscScalar, dimension(:), pointer :: array 17 PetscReal :: val 18 PetscErrorCode :: ierr 19 PetscInt :: zero = 0, one = 1 20 21 PetscCallA(PetscInitialize(PETSC_NULL_CHARACTER, ierr)) 22 PetscCallA(DMCreate(PETSC_COMM_WORLD, dm, ierr)) 23 PetscCallA(DMSetType(dm, DMPLEX, ierr)) 24 PetscCallA(DMSetFromOptions(dm, ierr)) 25 PetscCallA(DMViewFromOptions(dm, PETSC_NuLL_OBJECT, "-dm_view", ierr)) 26 PetscCallA(DMGetDimension(dm, dim, ierr)) 27 28 !!! Describe the solution variables that are discretized on the mesh 29 ! Create scalar field u and a vector field v 30 numFields = 2 31 numComp = [one, dim] 32 numDof = 0 33 !Let u be defined on cells 34 numDof(0*(dim + 1) + dim + 1) = 1 35 !Let v be defined on vertices 36 numDof(1*(dim + 1) + 1) = dim 37 !No boundary conditions */ 38 numBC = 0 39 40 !!! Create a PetscSection to handle the layout of the discretized variables 41 PetscCallA(DMSetNumFields(dm, numFields, ierr)) 42 PetscCallA(DMPlexCreateSection(dm, PETSC_NULL_DMLABEL_ARRAY, numComp, numDof, numBC, PETSC_NULL_INTEGER_ARRAY, PETSC_NULL_IS_ARRAY, PETSC_NULL_IS_ARRAY, PETSC_NULL_IS, section, ierr)) 43 ! Name the Field variables 44 PetscCallA(PetscSectionSetFieldName(section, zero, "u", ierr)) 45 PetscCallA(PetscSectionSetFieldName(section, one, "v", ierr)) 46 ! Tell the DM to use this data layout 47 PetscCallA(DMSetLocalSection(dm, section, ierr)) 48 49 !!! Construct the communication pattern for halo exchange between local vectors */ 50 ! Get the point SF: an object that says which copies of mesh points (cells, 51 ! vertices, faces, edges) are copies of points on other processes 52 PetscCallA(DMGetPointSF(dm, pointSF, ierr)) 53 ! Relate the locations of ghost degrees of freedom on this process 54 ! to their locations of the non-ghost copies on a different process 55 PetscCallA(PetscSFCreateRemoteOffsets(pointSF, section, section, remoteOffsets, ierr)) 56 ! Use that information to construct a star forest for halo exchange 57 ! for data described by the local section 58 PetscCallA(PetscSFCreateSectionSF(pointSF, section, remoteOffsets, section, sectionSF, ierr)) 59 if (associated(remoteOffsets)) then 60 PetscCallA(PetscSFDestroyRemoteOffsets(remoteOffsets, ierr)) 61 end if 62 63 !!! Demo of halo exchange 64 ! Create a Vec with this layout 65 PetscCallA(DMCreateLocalVector(dm, u, ierr)) 66 PetscCallA(PetscObjectSetName(u, "Local vector", ierr)) 67 PetscCallMPIA(MPI_Comm_rank(PETSC_COMM_WORLD, rank, ierr)) 68 ! Set all mesh values to the MPI rank 69 val = rank 70 PetscCallA(VecSet(u, val, ierr)) 71 ! Get the raw array of values 72 PetscCallA(VecGetArrayWrite(u, array, ierr)) 73 !!! HALO EXCHANGE 74 PetscCallA(PetscSFBcastBegin(sectionSF, MPIU_SCALAR, array, array, MPI_REPLACE, ierr)) 75 ! local work can be done between Begin() and End() 76 PetscCallA(PetscSFBcastEnd(sectionSF, MPIU_SCALAR, array, array, MPI_REPLACE, ierr)) 77 ! Restore the raw array of values 78 PetscCallA(VecRestoreArrayWrite(u, array, ierr)) 79 ! View the results: should show which process has the non-ghost copy of each degree of freedom 80 PetscCallA(PetscSectionVecView(section, u, PETSC_VIEWER_STDOUT_WORLD, ierr)) 81 PetscCallA(VecDestroy(u, ierr)) 82 83 PetscCallA(PetscSFDestroy(sectionSF, ierr)) 84 PetscCallA(PetscSectionDestroy(section, ierr)) 85 PetscCallA(DMDestroy(dm, ierr)) 86 PetscCallA(PetscFinalize(ierr)) 87end program ex14f90 88!/*TEST 89! # Test on a 1D mesh with overlap 90! test: 91! nsize: 3 92! requires: !complex 93! args: -dm_plex_dim 1 -dm_plex_box_faces 3 -dm_refine_pre 1 -petscpartitioner_type simple -dm_distribute_overlap 1 94! 95!TEST*/ 96