Designation: Non-Export Controlled Content
                Thanks for your response. Your second sentence is a little 
confusing. If my world group is P0,P1, visible on both processes, why wouldn't 
the sensorList contain P1 on both processes?


From: users [] On Behalf Of George 
Sent: Friday, October 14, 2016 5:44 PM
To: Open MPI Users
Subject: Re: [OMPI users] communications groups


Let's assume that you have started 2 processes, and that your sensorList is 
{1}. The worldgroup will then be {P0, P1}, which trimmed via the sensorList 
will give the sensorgroup {MPI_GROUP_EMPTY} on P0 and the sensorgroup {P1} on 
P1. As a result on P0 you will create a MPI_COMM_NULL communicator, while on P1 
you will have a valid communicator sensorComm (which will only contain P1). You 
cannot do a Barrier on an MPI_COMM_NULL communicator, which might explain the 
"invalid communicator" error you are getting.


On Fri, Oct 14, 2016 at 5:33 PM, Marlborough, Rick 
<<>> wrote:

Designation: Non-Export Controlled Content
                I have the following code setup. The sensorList is an array of 
ints of size 1. The value it contains is 1. My comm world size is 5. The call 
to MPI_Barrier fails every time with error "invalid communicator". This code is 
pretty much copied out of a text book. I must be doing something wrong. I just 
don't see it. Can anyone else spot my error? I am using v2.01 on red hat 6.5.


                MPI_Comm_group(MPI_COMM_WORLD, &worldgroup);
MPI_Group_incl(worldgroup, 1, sensorList, &sensorgroup);
MPI_Comm_create(MPI_COMM_WORLD, sensorgroup, &sensorComm);


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