[mpich-discuss] Issues with MPI_Comm_create

[Arthur Wu]

Thanks a lot Rajeev. It worked great!!

Arthur

--- Rajeev Thakur <thakur at mcs.anl.gov> wrote:

> MPI_Comm_create returns MPI_COMM_NULL to processes
> not in the group, in this
> case rank 0. So you need an if (myrank != 0) around
> the MPI_Comm_size.
> 
> Rajeev
> 
> 
> > -----Original Message-----
> > From: owner-mpich-discuss at mcs.anl.gov 
> > [mailto:owner-mpich-discuss at mcs.anl.gov] On Behalf
> Of Arthur Wu
> > Sent: Friday, March 07, 2008 12:48 PM
> > To: mpich-discuss at mcs.anl.gov
> > Cc: Arthur Wu
> > Subject: [mpich-discuss] Issues with
> MPI_Comm_create
> > 
> > 
> > Hi There,
> > 
> > I am trying to create a new communicator using the
> > following textbook code. However, the created
> > communicator is always MPI_COMM_NULL, as shown in
> the
> > runtime error message. Since I could not find any
> > example code in MPICH2 regarding communicator
> > creation, my questions is this: does MPICH2
> currently
> > support creation of new communicators?
> > 
> > Thanks a lot.
> > 
> > Arthur Wu
> > 
> > >  
> > > // create the worker communicator
> > >     MPI_Group world_group, work_group;
> > >     MPI_Comm  work_comm;
> > >     int       excl_ranks[2];
> > >     int nn=0;
> > >  
> > >     excl_ranks[0] = 1;
> > >     excl_ranks[1] = 2;
> > >     MPI_Comm_group(MPI_COMM_WORLD,
> &world_group);
> > >     MPI_Group_incl(world_group, 2, excl_ranks,
> > > &work_group);
> > >     MPI_Comm_create(MPI_COMM_WORLD, work_group,
> > > &work_comm);
> > >     MPI_Comm_size(work_comm, &nn);
> > >  
> > >     fprintf(stderr,  "Sub comm size = %i\n", nn
> );
> > >  
> > 
> > Runtime errors:
> > 
> > > 
> > > C:\public\bin>mpiexec -n 3 -machinefile
> Config.txt
> > > c:\public\bin\MpiApp.exe c:\t
> > > emp\mpi\7 input.txt output.txt log.txt
> > > Process   1 of 3 on
> > > B00123F4418EA.corp.bankofamerica.com (pid 2168)
> > > Process   0 of 3 on
> > > B00123F4418EA.corp.bankofamerica.com (pid 4440)
> > > Process   2 of 3 on
> > > B000BCD9949B9.corp.bankofamerica.com (pid 208)
> > >  
> > > job aborted:
> > > rank: node: exit code[: error message]
> > > 0: B00123F4418EA: 1: Fatal error in
> MPI_Comm_size:
> > > Invalid communicator,
> > > error s
> > > tack:
> > > MPI_Comm_size(112): MPI_Comm_size(MPI_COMM_NULL,
> > > size=000FED08) failed
> > > MPI_Comm_size(70).: Null communicator
> > > 1: B00123F4418EA: 1
> > > 2: b000bcd9949b9: 1
> > >  
> > >  
> > 
> > 
> >       
> >
>
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> > 
> 
> 



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