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mpi_comm_size(3openmpi) [osx man page]

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 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++ 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. 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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MPI_Comm_size(3)							MPI							  MPI_Comm_size(3)

NAME
MPI_Comm_size - Determines the size of the group associated with a communicator SYNOPSIS
int MPI_Comm_size( MPI_Comm comm, int *size ) INPUT PARAMETER
comm - communicator (handle) OUTPUT PARAMETER
size - number of processes in the group of comm (integer) NOTES
NULL HANDLES
The MPI 1.1 specification, in the section on opaque objects, explicitly disallows freeing a null communicator. The text from the standard is: A null handle argument is an erroneous IN argument in MPI calls, unless an exception is explicitly stated in the text that defines the function. Such exception is allowed for handles to request objects in Wait and Test calls (sections Communication Completion and Multiple Completions ). Otherwise, a null handle can only be passed to a function that allocates a new object and returns a reference to it in the handle. THREAD AND INTERRUPT SAFETY
This routine is both thread- and interrupt-safe. This means that this routine may safely be used by multiple threads and from within a signal handler. NOTES FOR FORTRAN
All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement. All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran. ERRORS
All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible. MPI_SUCCESS - No error; MPI routine completed successfully. MPI_ERR_COMM - Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank ). MPI_ERR_ARG - Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK ). LOCATION
comm_size.c 7/28/2010 MPI_Comm_size(3)
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