[mpich-discuss] MPI_Comm_Spawn question

[Dave Goodell]

On Jun 29, 2011, at 10:26 AM CDT, Eric Hui wrote:

> I started my MPI program with one process only and tried to use MPI_Comm_Spawn to launch three more copies like this:
...
> I am trying to join the parents and the children together into one group.
>  
> Do I need to call MPI_Intercomm_merge?  I thought the "InterComm" is already supposed to have size = 4 with rank = 0, 1, 2 and 3.

I only skimmed the code, but you will almost certainly need to call MPI_Intercomm_merge at least once in order to construct the intracommunicator that you want.  I recommend reading the MPI-2.2 standard carefully to understand the differences between intercommunicators and intracommunicators.

-Dave