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Subject: Re: [OMPI users] Scatter+Group Communicator Issue
From: Timothy Stitt (Timothy.Stitt.9_at_[hidden])
Date: 2012-03-06 08:32:03


Hi Nadia,

Thanks for the reply. This is were my confusion with the scatter command comes in. I was really hoping that MPI_Scatter would automagically ignore the ranks that are not part of the group communicator, since this test code is part of something more complicated were many sub-communicators are created over various combinations of ranks, and used in various collective routines. Do I really have to filter out manually the non-communicator ranks before I call the scatter...it would be really nice if the scatter command was 'smart' enough to do this for me by looking at the communicator that is passed to the routine.

Thanks again,

Tim.

On Mar 6, 2012, at 8:28 AM, <nadia.derbey_at_[hidden]<mailto:nadia.derbey_at_[hidden]>> wrote:

Isn't it because you're calling MPI_Scatter() even on rank 2 which is not part of your new_comm?

Regards,
Nadia

users-bounces_at_[hidden]<mailto:users-bounces_at_[hidden]> wrote on 03/06/2012 01:52:06 PM:

> De : Timothy Stitt <Timothy.Stitt.9_at_[hidden]<mailto:Timothy.Stitt.9_at_[hidden]>>
> A : "users_at_[hidden]<mailto:users_at_[hidden]>" <users_at_[hidden]<mailto:users_at_[hidden]>>
> Date : 03/06/2012 01:52 PM
> Objet : [OMPI users] Scatter+Group Communicator Issue
> Envoyé par : users-bounces_at_[hidden]<mailto:users-bounces_at_[hidden]>
>
> Hi all,
>
> I am scratching my head over what I think should be a relatively
> simple group communicator operation. I am hoping some kind person
> can put me out of my misery and figure out what I'm doing wrong.
>
> Basically, I am trying to scatter a set of values to a subset of
> process ranks (hence the need for a group communicator). When I run
> the sample code over 4 processes (and scattering to 3 processes), I
> am getting a group-communicator related error in the scatter operation:
>
> > [stats.crc.nd.edu:29285] *** An error occurred in MPI_Scatter
> > [stats.crc.nd.edu:29285] *** on communicator MPI_COMM_WORLD
> > [stats.crc.nd.edu:29285] *** MPI_ERR_COMM: invalid communicator
> > [stats.crc.nd.edu:29285] *** MPI_ERRORS_ARE_FATAL (your MPI job
> will now abort)
> > Complete - Rank 1
> > Complete - Rank 0
> > Complete - Rank 3
>
> The actual test code is below:
>
> program scatter_bug
>
> use mpi
>
> implicit none
>
> integer :: ierr,my_rank,procValues(3),procRanks(3)
> integer :: in_cnt,orig_group,new_group,new_comm,out
>
> call MPI_INIT(ierr)
> call MPI_COMM_RANK(MPI_COMM_WORLD,my_rank,ierr)
>
> procRanks=(/0,1,3/)
> procValues=(/0,434,268/)
> in_cnt=3
>
> ! Create sub-communicator
> call MPI_COMM_GROUP(MPI_COMM_WORLD, orig_group, ierr)
> call MPI_Group_incl(orig_group, in_cnt, procRanks, new_group, ierr)
> call MPI_COMM_CREATE(MPI_COMM_WORLD, new_group, new_comm, ierr)
>
> call MPI_SCATTER(procValues, 1, MPI_INTEGER, out, 1, MPI_INTEGER,
> 0, new_comm, ierr);
>
> print *,"Complete - Rank", my_rank
>
> end program scatter_bug
>
> Thanks in advance for any advice you can give.
>
> Regards.
>
> Tim.
> _______________________________________________
> users mailing list
> users_at_[hidden]<mailto:users_at_[hidden]>
> http://www.open-mpi.org/mailman/listinfo.cgi/users
<ATT00001..txt>

Tim Stitt PhD (User Support Manager).
Center for Research Computing | University of Notre Dame |
P.O. Box 539, Notre Dame, IN 46556 | Phone: 574-631-5287 | Email: tstitt_at_[hidden]<mailto:tstitt_at_[hidden]>