Newsgroups: comp.parallel.mpi
From: raja@rsn.hp.com (Raja Daoud)
Subject: Re: New Ranks after MPI_Comm_dup
Organization: Hewlett-Packard Co.
Date: 30 Nov 1997 00:20:27 -0600
Message-ID: <65r0jb$hm@tbag.rsn.hp.com>

Sanjay Velamparambil  <velampar@uiuc.edu> wrote:
>    will the processors have the same rank  under the new communicator
>after a call to MPI_Comm_dup?

Yes.  Page 145, lines 20-21:

"[MPI_COMM_DUP] Returns in newcomm a new communicator with the same
group, any copied cached information, but a new context."

The advice to implementors that follows this text informs that a new
copy of the group need not be created.  The old group could be used,
incrementing a reference count.  I imagine that most implementations,
particularly those based on LAM or MPICH, follow this advice.
Regards,

--Raja

-=-
Raja Daoud				Hewlett-Packard Co.
raja@rsn.hp.com				http://www.hp.com/go/mpi