Actual source code: ex1f.F90
petsc-3.13.6 2020-09-29
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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 petscvec
     11:       implicit none

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

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

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

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

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

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

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

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

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

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

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

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

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