1: !
  2: !
  3: !  Description:  Illustrates the use of VecSetValues() to set
  4: !  multiple values at once; demonstrates VecGetArray().
  5: !
  6: ! -----------------------------------------------------------------------
  7: #include <petsc/finclude/petscvec.h>
  8: program main
  9:   use petscvec
 10:   implicit none

 12: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 13: !                 Beginning of program
 14: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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

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

 26: !  Create initial vector and duplicate it

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

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

 35:   do i = 1, n
 36:     loc(i) = i - 1
 37:     xwork(i) = 10.0*real(i)
 38:   end do

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

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

 47: !  Assemble vector

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

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

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

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

 68: !  Modify vector data

 70:   do i = 1, n
 71:     xx_v(i) = 100.0*real(i)
 72:     yy_v(i) = 1000.0*real(i)
 73:   end do

 75: !  Restore vectors

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

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

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

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

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

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