On 12/3/21 12:09 PM, Jed Brown wrote:

Many find MPI_Comm_split() to be a more convenient interface. Yes, I don't think that will work for my case though, as my groups may overlap, and some processes may not be in any group.

I think the man page is fairly clear.

| MPI_Comm_create_group is similar to MPI_Comm_create; however, MPI_Comm_create must be called by all processes in the group of comm, whereas MPI_Comm_create_group must be called by all processes in group, which is a subgroup of the group of comm.

Yes, it looks like the mpitutorial.com example I followed was a bit misleading then. Thanks! - Adrian -- Dr Adrian Croucher Senior Research Fellow Department of Engineering Science University of Auckland, New Zealand email: [email protected] tel: +64 (0)9 923 4611