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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 inter-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



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