Actual source code: ex2f.F90
1: !
2: !
3: ! Description: Builds a parallel vector with 1 component on the first
4: ! processor, 2 on the second, etc. Then each processor adds
5: ! one to all elements except the last rank.
6: !
7: ! -----------------------------------------------------------------------
9: program main
10: #include <petsc/finclude/petscvec.h>
11: use petscvec
12: implicit none
14: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
15: ! Beginning of program
16: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
18: Vec x
19: PetscInt N, i, ione
20: PetscErrorCode ierr
21: PetscMPIInt rank
22: PetscScalar one, value(1)
24: PetscCallA(PetscInitialize(ierr))
25: one = 1.0
26: PetscCallMPIA(MPI_Comm_rank(PETSC_COMM_WORLD, rank, ierr))
28: ! Create a parallel vector.
29: ! - In this case, we specify the size of the local portion on
30: ! each processor, and PETSc computes the global size. Alternatively,
31: ! if we pass the global size and use PETSC_DECIDE for the
32: ! local size PETSc will choose a reasonable partition trying
33: ! to put nearly an equal number of elements on each processor.
35: N = rank + 1
36: ione = 1
37: PetscCallA(VecCreateFromOptions(PETSC_COMM_WORLD, PETSC_NULL_CHARACTER, ione, N, PETSC_DECIDE, x, ierr))
38: PetscCallA(VecGetSize(x, N, ierr))
39: PetscCallA(VecSet(x, one, ierr))
41: ! Set the vector elements.
42: ! - Note that VecSetValues() uses 0-based row and column numbers
43: ! in Fortran as well as in C.
44: ! - Always specify global locations of vector entries.
45: ! - Each processor can contribute any vector entries,
46: ! regardless of which processor "owns" them; any nonlocal
47: ! contributions will be transferred to the appropriate processor
48: ! during the assembly process.
49: ! - In this example, the flag ADD_VALUES indicates that all
50: ! contributions will be added together.
52: ione = 1
53: do 100 i = 0, N - rank - 1
54: PetscCallA(VecSetValues(x, ione, [i], [one], ADD_VALUES, ierr))
55: 100 continue
57: ! Assemble vector, using the 2-step process:
58: ! VecAssemblyBegin(), VecAssemblyEnd()
59: ! Computations can be done while messages are in transition
60: ! by placing code between these two statements.
62: PetscCallA(VecAssemblyBegin(x, ierr))
63: PetscCallA(VecAssemblyEnd(x, ierr))
65: ! Test VecGetValues() with scalar entries
66: if (rank == 0) then
67: ione = 0
68: PetscCallA(VecGetValues(x, ione, [i], value, ierr))
69: end if
71: ! View the vector; then destroy it.
73: PetscCallA(VecView(x, PETSC_VIEWER_STDOUT_WORLD, ierr))
74: PetscCallA(VecDestroy(x, ierr))
76: PetscCallA(PetscFinalize(ierr))
77: end
79: !/*TEST
80: !
81: ! test:
82: ! nsize: 2
83: ! filter: grep -v " MPI process"
84: !
85: !TEST*/