Actual source code: ex1f.F90
petsc-3.15.0 2021-03-30
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      2: !    Description: A star forest is a simple tree with one root and zero or more leaves.
      3: !    Many common communication patterns can be expressed as updates of rootdata using leafdata and vice-versa.
      4: !     This example creates a star forest, communicates values using the graph  views the graph, then destroys it.
      5: !
      6: !     This is a copy of ex1.c but currently only tests the broadcast operation

      8:       program main
      9: #include <petsc/finclude/petscvec.h>
     10:       use petscmpi  ! or mpi or mpi_f08
     11:       use petscvec
     12:       implicit none

     14:       PetscErrorCode                ierr
     15:       PetscInt                      i,nroots,nrootsalloc,nleaves,nleavesalloc,mine(6),stride
     16:       type(PetscSFNode)             remote(6)
     17:       PetscMPIInt                   rank,size
     18:       PetscSF                       sf
     19:       PetscInt                      rootdata(6),leafdata(6)

     21: ! used with PetscSFGetGraph()
     22:       type(PetscSFNode), pointer :: gremote(:)
     23:       PetscInt, pointer ::          gmine(:)
     24:       PetscInt                      gnroots,gnleaves;

     26:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
     27:       if (ierr .ne. 0) then
     28:         print*,'Unable to initialize PETSc'
     29:         stop
     30:       endif
     31:       stride = 2
     32:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr);CHKERRA(ierr)
     33:       call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr);CHKERRA(ierr)

     35:       if (rank == 0) then
     36:          nroots = 3
     37:       else
     38:          nroots = 2
     39:       endif
     40:       nrootsalloc  = nroots * stride;
     41:       if (rank > 0) then
     42:          nleaves = 3
     43:       else
     44:          nleaves = 2
     45:       endif
     46:       nleavesalloc = nleaves * stride
     47:       if (stride > 1) then
     48:          do i=1,nleaves
     49:             mine(i) = stride * (i-1)
     50:          enddo
     51:       endif

     53: ! Left periodic neighbor
     54:       remote(1)%rank  = modulo(rank+size-1,size)
     55:       remote(1)%index = 1 * stride
     56: ! Right periodic neighbor
     57:       remote(2)%rank  = modulo(rank+1,size)
     58:       remote(2)%index = 0 * stride
     59:       if (rank > 0) then !               All processes reference rank 0, index
     60:          remote(3)%rank  = 0
     61:          remote(3)%index = 2 * stride
     62:       endif

     64: !  Create a star forest for communication
     65:       call PetscSFCreate(PETSC_COMM_WORLD,sf,ierr);CHKERRA(ierr)
     66:       call PetscSFSetFromOptions(sf,ierr);CHKERRA(ierr)
     67:       call PetscSFSetGraph(sf,nrootsalloc,nleaves,mine,PETSC_COPY_VALUES,remote,PETSC_COPY_VALUES,ierr);CHKERRA(ierr)
     68:       call PetscSFSetUp(sf,ierr);CHKERRA(ierr)

     70: !   View graph, mostly useful for debugging purposes.
     71:       call PetscViewerPushFormat(PETSC_VIEWER_STDOUT_WORLD,PETSC_VIEWER_ASCII_INFO_DETAIL,ierr);CHKERRA(ierr)
     72:       call PetscSFView(sf,PETSC_VIEWER_STDOUT_WORLD,ierr);CHKERRA(ierr)
     73:       call PetscViewerPopFormat(PETSC_VIEWER_STDOUT_WORLD,ierr);CHKERRA(ierr)

     75: !   Allocate space for send and receive buffers. This example communicates PetscInt, but other types, including
     76: !     * user-defined structures, could also be used.
     77: !     Set rootdata buffer to be broadcast
     78:       do i=1,nrootsalloc
     79:          rootdata(i) = -1
     80:       enddo
     81:       do i=1,nroots
     82:          rootdata(1 + (i-1)*stride) = 100*(rank+1) + i - 1
     83:       enddo

     85: !     Initialize local buffer, these values are never used.
     86:       do i=1,nleavesalloc
     87:          leafdata(i) = -1
     88:       enddo

     90: !     Broadcast entries from rootdata to leafdata. Computation or other communication can be performed between the begin and end calls.
     91:       call PetscSFBcastBegin(sf,MPIU_INTEGER,rootdata,leafdata,MPI_REPLACE,ierr);CHKERRA(ierr)
     92:       call PetscSFBcastEnd(sf,MPIU_INTEGER,rootdata,leafdata,MPI_REPLACE,ierr);CHKERRA(ierr)
     93:       call PetscViewerASCIIPrintf(PETSC_VIEWER_STDOUT_WORLD,"## Bcast Rootdata\n",ierr);CHKERRA(ierr)
     94:       call PetscIntView(nrootsalloc,rootdata,PETSC_VIEWER_STDOUT_WORLD,ierr);CHKERRA(ierr)
     95:       call PetscViewerASCIIPrintf(PETSC_VIEWER_STDOUT_WORLD,"## Bcast Leafdata\n",ierr);CHKERRA(ierr)
     96:       call PetscIntView(nleavesalloc,leafdata,PETSC_VIEWER_STDOUT_WORLD,ierr);CHKERRA(ierr)

     98:       call PetscSFGetGraph(sf,gnroots,gnleaves,gmine,gremote,ierr);CHKERRA(ierr)
     99:       if (gnleaves .ne. nleaves) then; SETERRA(PETSC_COMM_WORLD,PETSC_ERR_PLIB,'nleaves returned from PetscSFGetGraph() does not match that set with PetscSFSetGraph()'); endif
    100:       do i=1,nleaves
    101:          if (gmine(i) .ne. mine(i)) then; SETERRA(PETSC_COMM_WORLD,PETSC_ERR_PLIB,'Root from PetscSFGetGraph() does not match that set with PetscSFSetGraph()'); endif
    102:       enddo
    103:       do i=1,nleaves
    104:          if (gremote(i)%index .ne. remote(i)%index) then; SETERRA(PETSC_COMM_WORLD,PETSC_ERR_PLIB,'Leaf from PetscSFGetGraph() does not match that set with PetscSFSetGraph()'); endif
    105:       enddo

    107:       deallocate(gremote)
    108: !    Clean storage for star forest.
    109:       call PetscSFDestroy(sf,ierr);CHKERRA(ierr)
    110:       call PetscFinalize(ierr);
    111:   end

    113: !/*TEST
    114: !  build:
    115: !    requires: define(PETSC_HAVE_FORTRAN_TYPE_STAR)
    116: !
    117: !  test:
    118: !    nsize: 3
    119: !
    120: !TEST*/