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MPI_Comm_size(3) man page (version 1.2.9)

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NAME

       MPI_Comm_size  - Returns the size of the group associated with a commu-
       nicator.

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  communi-
       cator.  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  communica-
       tor   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++ func-
       tions 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.

SEE ALSO

       MPI_Comm_group
       MPI_Comm_rank
       MPI_Comm_compare

Open MPI 1.2                    September 2006         MPI_Comm_size(3OpenMPI)

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