The following are all local operations.
| MPI_COMM_SIZE(comm, size) | |
| IN comm | communicator (handle) |
| OUT size | number of processes in the group of comm (integer) |
int MPI_Comm_size(MPI_Comm comm, int *size)
MPI_Comm_size(comm, size, ierror)
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, INTENT(OUT) :: size
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_COMM_SIZE(COMM, SIZE, IERROR)
INTEGER COMM, SIZE, IERROR
Rationale.
This function is equivalent to accessing the communicator's group with
MPI_COMM_GROUP (see above), computing the size using
MPI_GROUP_SIZE,
and then freeing the temporary group via MPI_GROUP_FREE. However,
this function is so commonly used that this shortcut was introduced.
( End of rationale.)
Advice to users.
This function indicates the number of processes involved in a communicator. For MPI_COMM_WORLD, it indicates the total number of processes available unless the number of processes has been changed by using the functions described in Chapter Process Creation and Management ; note that the number of processes in MPI_COMM_WORLD does not change during the life of an MPI program.
This call is often used with the next call to determine the amount of
concurrency available for a specific library or program. The following
call, MPI_COMM_RANK indicates the rank of the process
that calls it in the range from 0... size-1, where size
is the return value of MPI_COMM_SIZE. ( End of advice to users.)
| MPI_COMM_RANK(comm, rank) | |
| IN comm | communicator (handle) |
| OUT rank | rank of the calling process in group of comm (integer) |
int MPI_Comm_rank(MPI_Comm comm, int *rank)
MPI_Comm_rank(comm, rank, ierror)
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, INTENT(OUT) :: rank
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_COMM_RANK(COMM, RANK, IERROR)
INTEGER COMM, RANK, IERROR
Rationale.
This function is equivalent to accessing the communicator's group with
MPI_COMM_GROUP (see above), computing the rank using
MPI_GROUP_RANK,
and then freeing the temporary group via MPI_GROUP_FREE. However,
this function is so commonly used that this shortcut was introduced.
( End of rationale.)
Advice to users.
This function gives the rank of the process in the particular communicator's group. It is useful, as noted above, in conjunction with MPI_COMM_SIZE.
Many programs will be written with the master-slave model, where one process
(such as the rank-zero process) will play a supervisory role, and the other
processes will serve as compute nodes. In this framework, the two preceding
calls are useful for determining the roles of the various processes of a
communicator.
( End of advice to users.)
| MPI_COMM_COMPARE(comm1, comm2, result) | |
| IN comm1 | first communicator (handle) |
| IN comm2 | second communicator (handle) |
| OUT result | result (integer) |
int MPI_Comm_compare(MPI_Comm comm1, MPI_Comm comm2, int *result)
MPI_Comm_compare(comm1, comm2, result, ierror)
TYPE(MPI_Comm), INTENT(IN) :: comm1, comm2
INTEGER, INTENT(OUT) :: result
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_COMM_COMPARE(COMM1, COMM2, RESULT, IERROR)
INTEGER COMM1, COMM2, RESULT, IERROR
MPI_IDENT results if and only if comm1 and comm2 are handles for the same object (identical groups and same contexts). MPI_CONGRUENT results if the underlying groups are identical in constituents and rank order; these communicators differ only by context. MPI_SIMILAR results if the group members of both communicators are the same but the rank order differs. MPI_UNEQUAL results otherwise.