# Commgroup Type

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The commgroup[a,b,c] (where a,b and c are PIDS) type allows the programmer to specify a subset of processes within a communication group. This type is used within the multiple type, and apart from limiting the physical allocation of data will create an MPI communication group which is used for communications of that variable.

## Examples

var a:Int::allocated[multiple[commgroup[1,3,5]]];
var l:Int::allocated[single[on[1]]];
a:=l;
In this example variable a is allocated to processes 1,3 and 5. The third line (assignment) will result in an MPI broadcast, but only using the group of processes 1,3 and 5. If variable l was not allocated on a process in the communication group of a then this assignment would result in an error.
Last Modified: August 2008