Hi guys
I'm having a little trouble using MPI_IN_PLACE with MPI_REDUCE /
MPI_ALLREDUCE in Fortran. If I try to MPI_IN_PLACE with C bindings it
works fine running on 2 nodes:
Result:
3.000000 3.000000 3.000000 3.000000
Regardless of using MPI_Reduce or MPI_Allreduce. However, this fails
for the fortran version:
Result:
2.000000 2.000000 2.000000 2.000000
Apparently, MPI is ignoring values from the root node. Here's the
source for the Fortran code:
---
program inplace
use mpi
implicit none
integer :: ierr, rank, rsize, bsize
real, dimension( 2, 2 ) :: buffer, out
integer :: rc
call MPI_INIT(ierr)
call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr)
call MPI_COMM_SIZE(MPI_COMM_WORLD, rsize, ierr)
buffer = rank + 1
bsize = size(buffer,1) * size(buffer,2)
if ( rank == 0 ) then
call mpi_reduce( MPI_IN_PLACE, buffer, bsize, MPI_REAL, MPI_SUM,
0, MPI_COMM_WORLD, ierr )
else
call mpi_reduce( buffer, 0, bsize, MPI_REAL, MPI_SUM,
0, MPI_COMM_WORLD, ierr )
endif
! use allreduce instead
! call mpi_allreduce( MPI_IN_PLACE, buffer, bsize, MPI_REAL,
MPI_SUM, MPI_COMM_WORLD, ierr )
if ( rank == 0 ) then
print *, 'Result:'
print *, buffer
endif
rc = 0
call mpi_finalize( rc )
end program
---
Any ideas?
Cheers,
Ricardo
---
Prof. Ricardo Fonseca
GoLP - Grupo de Lasers e Plasmas
Instituto de Plasmas e Fusão Nuclear
Instituto Superior Técnico
Av. Rovisco Pais
1049-001 Lisboa
Portugal
tel: +351 21 8419202
fax: +351 21 8464455
web: http://cfp.ist.utl.pt/golp/
