C -*- Mode: Fortran; -*- 

C

C  (C) 2011 by Argonne National Laboratory.

C      See COPYRIGHT in top-level directory.

C

      subroutine uop( cin, cout, count, datatype )

      implicit none

      include 'mpif.h'

      integer cin(*), cout(*)

      integer count, datatype

      integer i

      if (datatype .ne. MPI_INTEGER) then

         write(6,*) 'Invalid datatype ',datatype,' passed to user_op()'

         return

      endif

      do i=1, count

         cout(i) = cin(i) + cout(i)

      enddo

      end

C

C Test of reduce scatter.

C

C Each processor contributes its rank + the index to the reduction, 

C then receives the ith sum

C

C Can be called with any number of processors.

C

      program main

      implicit none

      include 'mpif.h'

      integer errs, ierr, toterr

      integer maxsize

      parameter (maxsize=1024)

      integer sendbuf(maxsize), recvbuf, recvcounts(maxsize)

      integer size, rank, i, sumval

      integer comm, sumop

      external uop

      errs = 0

      call mtest_init( ierr )

      comm = MPI_COMM_WORLD

      call mpi_comm_size( comm, size, ierr )

      call mpi_comm_rank( comm, rank, ierr )

      if (size .gt. maxsize) then

      endif

      do i=1, size

         sendbuf(i) = rank + i - 1

         recvcounts(i) = 1

      enddo

      call mpi_reduce_scatter( sendbuf, recvbuf, recvcounts, 

     &     MPI_INTEGER, MPI_SUM, comm, ierr )

      sumval = size * rank + ((size - 1) * size)/2

C recvbuf should be size * (rank + i) 

      if (recvbuf .ne. sumval) then

         errs = errs + 1

         print *, "Did not get expected value for reduce scatter"

         print *, rank, " Got ", recvbuf, " expected ", sumval

      endif

      call mpi_op_create( uop, .true., sumop, ierr )

      call mpi_reduce_scatter( sendbuf, recvbuf, recvcounts, 

     &     MPI_INTEGER, sumop, comm, ierr )

      sumval = size * rank + ((size - 1) * size)/2

C recvbuf should be size * (rank + i) 

      if (recvbuf .ne. sumval) then

         errs = errs + 1

         print *, "sumop: Did not get expected value for reduce scatter"

         print *, rank, " Got ", recvbuf, " expected ", sumval

      endif

      call mpi_op_free( sumop, ierr )

      call mtest_finalize( errs )

      call mpi_finalize( ierr )

      end