MPI_Comm_size(3) Open MPI MPI_Comm_size(3)NAMEMPI_Comm_size - Returns the size of the group associated with a commu‐
nicator.
SYNTAXC 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 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++ 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
1.7.4 Feb 04, 2014 MPI_Comm_size(3)
