MPI_Comm_size(3)                   Open MPI                   MPI_Comm_size(3)



NAME
       MPI_Comm_size  - Returns the size of the group associated with a
       communicator.


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Comm_size(MPI_Comm comm, int *size)


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_COMM_SIZE(COMM, SIZE, IERROR)
            INTEGER   COMM, SIZE, IERROR


C++ Syntax
       #include <mpi.h>
       int Comm::Get_size() const


INPUT PARAMETER
       comm      Communicator (handle).


OUTPUT PARAMETERS
       size      Number of processes in the group of comm (integer).

       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       This function indicates the number of processes involved in a
       communicator. For MPI_COMM_WORLD, it indicates the total number of
       processes available. This function is equivalent to accessing the
       communicator's group with MPI_Comm_group, computing the size using
       MPI_Group_size, and then freeing the temporary group via
       MPI_Group_free. If the communicator is an intra-communicator (enables
       communication between two groups), this function returns the size of
       the local group.  To return the size of the remote group, use the
       MPI_Comm_remote_size function.

       This call is often used with MPI_Comm_rank to determine the amount of
       concurrency available for a specific library or program. 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.


NOTE
       MPI_COMM_NULL is not considered a valid argument to this function.


ERRORS
       Almost all MPI routines return an error value; C routines as the value
       of the function and Fortran routines in the last argument. C++
       functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       Before the error value is returned, the current MPI error handler is
       called. By default, this error handler aborts the MPI job, except for
       I/O function errors. The error handler may be changed with
       MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN
       may be used to cause error values to be returned. Note that MPI does
       not guarantee that an MPI program can continue past an error.


SEE ALSO
       MPI_Comm_group
       MPI_Comm_rank
       MPI_Comm_compare




1.4.1                            Jan 14, 2010                 MPI_Comm_size(3)
