Actual source code: ex12f.F90

  1: program main

  3: #include <petsc/finclude/petscvec.h>

  5:   use petscvec
  6:   implicit none

  8:   PetscErrorCode ierr
  9:   Vec v, s
 10:   PetscInt, parameter ::      n = 20
 11:   PetscScalar, parameter ::   sone = 1.0
 12:   PetscBool :: flg
 13:   PetscInt, parameter :: zero = 0, one = 1, two = 2

 15:   PetscCallA(PetscInitialize(ierr))

 17:   PetscCallA(PetscOptionsGetInt(PETSC_NULL_OPTIONS, PETSC_NULL_CHARACTER, '-n', n, flg, ierr))

 19:   ! Create multi-component vector with 2 components
 20:   PetscCallA(VecCreate(PETSC_COMM_WORLD, v, ierr))
 21:   PetscCallA(VecSetSizes(v, PETSC_DECIDE, n, ierr))
 22:   PetscCallA(VecSetBlockSize(v, two, ierr))
 23:   PetscCallA(VecSetFromOptions(v, ierr))

 25:   ! Create single-component vector
 26:   PetscCallA(VecCreate(PETSC_COMM_WORLD, s, ierr))
 27:   PetscCallA(VecSetSizes(s, PETSC_DECIDE, n/2, ierr))
 28:   PetscCallA(VecSetFromOptions(s, ierr))

 30:   !Set the vectors to entries to a constant value.
 31:   PetscCallA(VecSet(v, sone, ierr))

 33:   !Get the first component from the multi-component vector to the single vector
 34:   PetscCallA(VecStrideGather(v, zero, s, INSERT_VALUES, ierr))

 36:   PetscCallA(VecView(s, PETSC_VIEWER_STDOUT_WORLD, ierr))

 38:   !Put the values back into the second component
 39:   PetscCallA(VecStrideScatter(s, one, v, ADD_VALUES, ierr))

 41:   PetscCallA(VecView(v, PETSC_VIEWER_STDOUT_WORLD, ierr))

 43:   ! Free work space.All PETSc objects should be destroyed when they are no longer needed.
 44:   PetscCallA(VecDestroy(v, ierr))
 45:   PetscCallA(VecDestroy(s, ierr))
 46:   PetscCallA(PetscFinalize(ierr))

 48: end program

 50: !/*TEST
 51: !
 52: !     test:
 53: !       nsize: 2
 54: !       output_file: output/ex12_1.out
 55: !
 56: !TEST*/