[MPICH] semantic question re: groups

[David Minor]

Hello Newslist,

I have a master process that gathers replies from all of its slave
processes, then on the basis of the replies it needs to do a collective
operation on a sub-set of the slave processes.  What's the cleanest way to
do this?
I can create a group on the master process and then a communicator from the
group, but the slave processes cannot create the same communicator
without the duplicate global information that the master process holds.
Each slave process only knows whether it is going to participate in the
collective operation but it doesn't know anything about the other processes
participating except the master process.

I could do this of course with point-to-point operations, but it seems there
should be a neater way.  Any suggestions? 

David Minor
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