Subject: copying ?

From: [email-masked]
Date: Mon, 6 Sep 93 23:36:46 PDT

I have a couple of questions about copying groups and communicators.

1. The current context chapter says that MPI_GROUP_DUP is "essential to
   the support of virtual topologies".  I do not understand this, and
   the examples are of no help.  (Only one example calls MPI_COMM_DUP,
   and no example calls MPI_GROUP_DUP.)  

   Can someone please explain why MPI_GROUP_DUP is considered so
   important, and perhaps provide an illustrative example?

2. The chapter says that MPI_COMM_{,LOCAL_,COLL_}DUP "duplicates
   the existing communicator comm with all its cached information,
   replacing just the context, and creates the new communicator
   new_comm".

   Does a communicator bind a group by reference or by copy?
   That is, does dup'ing a communicator imply dup'ing its group?

   I would hope that the group is bound by reference, but it
   needs to be explicit one way or the other.

--Rik
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[email-masked] (alias 'd39135')   Rik Littlefield
Tel: 509-375-3927                         Pacific Northwest Lab, MS K1-87
Fax: 509-375-6631                         P.O.Box 999, Richland, WA  99352