## 5.6.1. Inter-communicator Accessors

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MPI_COMM_TEST_INTER(comm, flag)
[ IN comm] communicator (handle)
[ OUT flag] (logical)

`int MPI_Comm_test_inter(MPI_Comm comm, int *flag)
`

`MPI_COMM_TEST_INTER(COMM, FLAG, IERROR)
INTEGER COMM, IERROR
LOGICAL FLAG
`

This local routine allows the calling process to determine if a communicator is an inter-communicator or an intra-communicator. It returns true if it is an inter-communicator, otherwise false.

When an inter-communicator is used as an input argument to the communicator accessors described above under intra-communication, the following table describes behavior.

Furthermore, the operation MPI_COMM_COMPARE is valid for inter-communicators. Both communicators must be either intra- or inter-communicators, or else MPI_UNEQUAL results. Both corresponding local and remote groups must compare correctly to get the results MPI_CONGRUENT and MPI_SIMILAR. In particular, it is possible for MPI_SIMILAR to result because either the local or remote groups were similar but not identical.

The following accessors provide consistent access to the remote group of an inter-communicator:

The following are all local operations.

MPI_COMM_REMOTE_SIZE(comm, size)
[ IN comm] inter-communicator (handle)
[ OUT size] number of processes in the remote group of comm (integer)

`int MPI_Comm_remote_size(MPI_Comm comm, int *size)
`

`MPI_COMM_REMOTE_SIZE(COMM, SIZE, IERROR)
INTEGER COMM, SIZE, IERROR
`

MPI_COMM_REMOTE_GROUP(comm, group)
[ IN comm] inter-communicator (handle)
[ OUT group] remote group corresponding to comm (handle)

`int MPI_Comm_remote_group(MPI_Comm comm, MPI_Group *group)
`

`MPI_COMM_REMOTE_GROUP(COMM, GROUP, IERROR)
INTEGER COMM, GROUP, IERROR
`

[] Rationale.

Symmetric access to both the local and remote groups of an inter-communicator is important, so this function, as well as MPI_COMM_REMOTE_SIZE have been provided. ( End of rationale.)

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