1: static char help[] = "Demonstrates VecStrideSum().\n\n";

  3: /*
  4:   Include "petscvec.h" so that we can use vectors.  Note that this file
  5:   automatically includes:
  6:      petscsys.h       - base PETSc routines   petscis.h     - index sets
  7:      petscviewer.h - viewers
  8: */

 10: #include <petscvec.h>

 12: int main(int argc, char **argv)
 13: {
 14:   Vec         x; /* vectors */
 15:   PetscScalar sum;
 16:   PetscInt    n   = 20;
 17:   PetscScalar one = 1.0;

 19:   PetscFunctionBeginUser;
 20:   PetscCall(PetscInitialize(&argc, &argv, (char *)0, help));
 21:   PetscCall(PetscOptionsGetInt(NULL, NULL, "-n", &n, NULL));

 23:   /*
 24:      Create a vector, specifying only its global dimension.
 25:      When using VecCreate(), VecSetSizes() and VecSetFromOptions(),
 26:      the vector format (currently parallel,
 27:      shared, or sequential) is determined at runtime.  Also, the parallel
 28:      partitioning of the vector is determined by PETSc at runtime.
 29:   */
 30:   PetscCall(VecCreate(PETSC_COMM_WORLD, &x));
 31:   PetscCall(VecSetSizes(x, PETSC_DECIDE, n));
 32:   PetscCall(VecSetBlockSize(x, 2));
 33:   PetscCall(VecSetFromOptions(x));

 35:   /*
 36:      Set the subvector entries to a constant value.
 37:   */
 38:   PetscCall(VecSet(x, one));
 39:   PetscCall(VecStrideScale(x, 1, -2));

 41:   PetscCall(VecSum(x, &sum));
 42:   PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Sum of entire vector: %g\n", (double)PetscRealPart(sum)));

 44:   PetscCall(VecStrideSum(x, 0, &sum));
 45:   PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Sum of sub-vector 0: %g\n", (double)PetscRealPart(sum)));

 47:   PetscCall(VecStrideSum(x, 1, &sum));
 48:   PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Sum of sub-vector 1: %g\n", (double)PetscRealPart(sum)));

 50:   /*
 51:      Free work space.  All PETSc objects should be destroyed when they
 52:      are no longer needed.
 53:   */
 54:   PetscCall(VecDestroy(&x));
 55:   PetscCall(PetscFinalize());
 56:   return 0;
 57: }

 59: /*TEST

 61:      test:
 62:        nsize: 2

 64: TEST*/