osx man page for mpi_group_size

MPI_Group_size(3OpenMPI)												  MPI_Group_size(3OpenMPI)

NAME
       MPI_Group_size - Returns the size of a group.

SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Group_size(MPI_Group group, int *size)

Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_GROUP_SIZE(GROUP, SIZE, IERROR)
	    INTEGER   GROUP, SIZE, IERROR

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

INPUT PARAMETERS
       group	 Group (handle).

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

       IERROR	 Fortran only: Error status (integer).

DESCRIPTION
       MPI_Group_size  returns in size the number of processes in the group. Thus, if group = MPI_GROUP_EMPTY, then the call will return size = 0.
       On the other hand, a call with group = MPI_GROUP_NULL is erroneous.

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.

       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.

Open MPI 1.2							  September 2006					  MPI_Group_size(3OpenMPI)