CODEWITHSUNDEEP
fortranmpi
Pradeep Kumar Jha
Pradeep Kumar Jha

Reputation: 877

MPI_REDUCE error

I dont understand why the following program is not working. When I am running it with "mpirun -np 2 a.out" I would expect it to print "N: 2" but instead it is giving me a seg fault.

Thank you

main.f

  program main

  implicit none

  include 'mpif.h'

  integer me, ngs,ierror

  call  inimpi(me, ngs)

  call calc

  call mpi_finalize( ierror )

  stop
  end

inimpi.f

  subroutine  inimpi(me, ngs)

  include  'mpif.h'

  integer me, ngs, ierror

  call  mpi_init( ierror )
  call  mpi_comm_rank( mpi_comm_world, me,  ierror )
  call  mpi_comm_size( mpi_comm_world, ngs, ierror )

  return
  end

calc.f

  subroutine  calc

  include 'mpif.h'

  integer  p, e, ierror

  p = 1

  call mpi_reduce(p, e, 1, mpi_integer,
 &     mpi_sum, mpi_comm_world, ierror)

  print *, "N: ", e
  return
  end

Upvotes: 0

Views: 912

Answers (1)

none_00
none_00

Reputation: 196

Taken from the mpich2 documentation:

int MPI_Reduce(void *sendbuf, void *recvbuf, int count, MPI_Datatype datatype, 
               MPI_Op op, int root, MPI_Comm comm)

You didn't specify the root for mpi_reduce. Because of this, mpi_comm_world is used as root and ierror is used as MPI_Comm. Did you mean to use MPI_Allreduce, which doesn't need a root argument?

Oh, and try to use use mpi instead of include 'mpif.h' if possible, this might have even caught the current error.

Upvotes: 3

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