[MPICH] Changing the comm size at runtime

[Rajeev Thakur]

> You can use all MPI communication functions, including collectives. It
will
> be the intercommunicator version of the collectives defined in MPI-2, as
the
> communicator returned by a connect-accept is an intercommunicator.

I should point out that you can also create an intracommunicator from an
intercommunicator by using MPI_Intercomm_merge and then use the regular
intracommunicator collectives if that's what you need.

Rajeev