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From: Murat Knecht (murat.knecht_at_[hidden])
Date: 2007-10-18 16:36:29


Hi,
I have a question regarding merging intracommunicators.
Using MPI_Spawn, I create on designated machines child processes,
retrieving an intercommunicator each time.
With MPI_Intercomm_Merge it is possible to get an intracommunicator
containing the master process(es) and the newly spawned child process.
The problem is to merge the intracommunicators into a single one.

I understand there is the possibilty to use the so created
intracommunicator from the first try in order to spawn the second child,
merge this one into the intracomm and continue like this.
This brings some considerable adminstrative overhead with it, as all
already spawned children must (be informed to) participate in the spawn
call.
I would rather merge all intercommunicators together in the end using
only the master process for spawning.
Both these possibilites have been mentioned in the following post.

http://www.lam-mpi.org/MailArchives/lam/2003/06/6226.php

While I understand the first one, I do not follow the second - I cannot
seem to find any method to merge multiple inter- or intracomms into a
single intracomm.
Groups cannot be used either, to collect the children and retrieve the
intracomm, because this is only used for subgrouping within an already
existing intracommunicator-group.
Is there a way to merge them the easy way, or did I misread the post above?

Thanks & best regards,
Murat