Date: 2025-03-28T21:11:23+00:00

Actual source code: ex8f.F90

      1: !
      2: ! Description: Demonstrates using a local ordering to set values into a parallel vector
      3: !

      5:   program main
      6: #include <petsc/finclude/petscvec.h>
      7:   use petscvec

      9:   implicit none

     11:   PetscErrorCode ierr
     12:   PetscMPIInt    rank
     13:   PetscInt    ::   i,ng,rstart,rend,M
     14:   PetscInt, pointer, dimension(:) :: gindices
     15:   PetscScalar, parameter :: sone = 1.0
     16:   Vec   ::         x
     17:   ISLocalToGlobalMapping :: ltog
     18:   PetscInt,parameter :: one = 1

     20:   PetscCallA(PetscInitialize(ierr))
     21:   PetscCallMPIA(MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr))

     23: !
     24: !     Create a parallel vector.
     25: !      - In this case, we specify the size of each processor's local
     26: !        portion, and PETSc computes the global size.  Alternatively,
     27: !        PETSc could determine the vector's distribution if we specify
     28: !        just the global size.
     29: !
     30:   PetscCallA(VecCreate(PETSC_COMM_WORLD,x,ierr))
     31:   PetscCallA(VecSetSizes(x,rank+one,PETSC_DECIDE,ierr))
     32:   PetscCallA(VecSetFromOptions(x,ierr))

     34:   PetscCallA(VecSet(x,sone,ierr))

     36: !
     37: !     Set the local to global ordering for the vector. Each processor
     38: !     generates a list of the global indices for each local index. Note that
     39: !     the local indices are just whatever is convenient for a particular application.
     40: !     In this case we treat the vector as lying on a one dimensional grid and
     41: !     have one ghost point on each end of the blocks owned by each processor.
     42: !

     44:   PetscCallA(VecGetSize(x,M,ierr))
     45:   PetscCallA(VecGetOwnershipRange(x,rstart,rend,ierr))
     46:   ng = rend - rstart + 2
     47:   allocate(gindices(0:ng-1))
     48:   gindices(0) = rstart -1

     50:   do i=0,ng-2
     51:    gindices(i+1) = gindices(i) + 1
     52:   end do

     54: ! map the first and last point as periodic

     56:   if (gindices(0) == -1) gindices(0) = M - 1

     58:   if (gindices(ng-1) == M) gindices(ng-1) = 0

     60:   PetscCallA(ISLocalToGlobalMappingCreate(PETSC_COMM_SELF,one,ng,gindices,PETSC_COPY_VALUES,ltog,ierr))
     61:   PetscCallA(VecSetLocalToGlobalMapping(x,ltog,ierr))
     62:   PetscCallA(ISLocalToGlobalMappingDestroy(ltog,ierr))
     63:   deallocate(gindices)

     65:      ! Set the vector elements.
     66:      ! - In this case set the values using the local ordering
     67:      ! - Each processor can contribute any vector entries,
     68:      !   regardless of which processor "owns" them; any nonlocal
     69:      !   contributions will be transferred to the appropriate processor
     70:      !   during the assembly process.
     71:      ! - In this example, the flag ADD_VALUES indicates that all
     72:      !   contributions will be added together.

     74:   do i=0,ng-1
     75:    PetscCallA(VecSetValuesLocal(x,one,[i],[sone],ADD_VALUES,ierr))
     76:   end do

     78:   !
     79:   ! Assemble vector, using the 2-step process:
     80:   ! VecAssemblyBegin(), VecAssemblyEnd()
     81:   ! Computations can be done while messages are in transition
     82:   ! by placing code between these two statements.
     83:   !
     84:   PetscCallA(VecAssemblyBegin(x,ierr))
     85:   PetscCallA(VecAssemblyEnd(x,ierr))
     86:   !
     87:   ! View the vector; then destroy it.
     88:   !
     89:   PetscCallA(VecView(x,PETSC_VIEWER_STDOUT_WORLD,ierr))
     90:   PetscCallA(VecDestroy(x,ierr))
     91:   PetscCallA(PetscFinalize(ierr))

     93: end program

     95: !/*TEST
     96: !
     97: !     test:
     98: !       nsize: 4
     99: !       output_file: output/ex8_1.out
    100: !
    101: !TEST*/