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MPI_Comm_size(3OpenMPI)                                                              MPI_Comm_size(3OpenMPI)



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  com-municator's communicator's
       municator'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  communica-tion communication
       tion  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




Open MPI 1.2                                   September 2006                        MPI_Comm_size(3OpenMPI)