Date: 2026-03-01T05:25:27+00:00

Actual source code: ex4f.F90

      1: !
      2: !
      3: !  Description:  Illustrates the use of VecSetValues() to set
      4: !  multiple values at once; demonstrates VecGetArray().
      5: !
      6: ! -----------------------------------------------------------------------

      8: program main
      9: #include <petsc/finclude/petscvec.h>
     10:   use petscvec
     11:   implicit none

     13: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     14: !                 Beginning of program
     15: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     17:   PetscScalar xwork(6)
     18:   PetscScalar, pointer :: xx_v(:), yy_v(:)
     19:   PetscInt i, n, loc(6), isix
     20:   PetscErrorCode ierr
     21:   Vec x, y

     23:   PetscCallA(PetscInitialize(ierr))
     24:   n = 6
     25:   isix = 6

     27: !  Create initial vector and duplicate it

     29:   PetscCallA(VecCreateSeq(PETSC_COMM_SELF, n, x, ierr))
     30:   PetscCallA(VecDuplicate(x, y, ierr))

     32: !  Fill work arrays with vector entries and locations.  Note that
     33: !  the vector indices are 0-based in PETSc (for both Fortran and
     34: !  C vectors)

     36:   do 10 i = 1, n
     37:     loc(i) = i - 1
     38:     xwork(i) = 10.0*real(i)
     39: 10  continue

     41: !  Set vector values.  Note that we set multiple entries at once.
     42: !  Of course, usually one would create a work array that is the
     43: !  natural size for a particular problem (not one that is as long
     44: !  as the full vector).

     46:     PetscCallA(VecSetValues(x, isix, loc, xwork, INSERT_VALUES, ierr))

     48: !  Assemble vector

     50:     PetscCallA(VecAssemblyBegin(x, ierr))
     51:     PetscCallA(VecAssemblyEnd(x, ierr))

     53: !  View vector
     54:     PetscCallA(PetscObjectSetName(x, 'initial vector:', ierr))
     55:     PetscCallA(VecView(x, PETSC_VIEWER_STDOUT_SELF, ierr))
     56:     PetscCallA(VecCopy(x, y, ierr))

     58: !  Get a pointer to vector data.
     59: !    - For default PETSc vectors, VecGetArray() returns a pointer to
     60: !      the data array.  Otherwise, the routine is implementation dependent.
     61: !    - You MUST call VecRestoreArray() when you no longer need access to
     62: !      the array.
     63: !    - Note that the Fortran interface to VecGetArray() differs from the
     64: !      C version.  See the users manual for details.

     66:     PetscCallA(VecGetArray(x, xx_v, ierr))
     67:     PetscCallA(VecGetArray(y, yy_v, ierr))

     69: !  Modify vector data

     71:     do 30 i = 1, n
     72:       xx_v(i) = 100.0*real(i)
     73:       yy_v(i) = 1000.0*real(i)
     74: 30    continue

     76: !  Restore vectors

     78:       PetscCallA(VecRestoreArray(x, xx_v, ierr))
     79:       PetscCallA(VecRestoreArray(y, yy_v, ierr))

     81: !  View vectors
     82:       PetscCallA(PetscObjectSetName(x, 'new vector 1:', ierr))
     83:       PetscCallA(VecView(x, PETSC_VIEWER_STDOUT_SELF, ierr))

     85:       PetscCallA(PetscObjectSetName(y, 'new vector 2:', ierr))
     86:       PetscCallA(VecView(y, PETSC_VIEWER_STDOUT_SELF, ierr))

     88: !  Free work space.  All PETSc objects should be destroyed when they
     89: !  are no longer needed.

     91:       PetscCallA(VecDestroy(x, ierr))
     92:       PetscCallA(VecDestroy(y, ierr))
     93:       PetscCallA(PetscFinalize(ierr))
     94:     end

     96: !/*TEST
     97: !
     98: !     test:
     99: !
    100: !TEST*/