Date: 2025-03-28T21:11:23+00:00

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 .eq. 0) then
     67:         ione = 0
     68:         PetscCallA(VecGetValues(x,ione,[i],value,ierr))
     69:       endif

     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*/