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MPI_Comm_size - Returns the size of the group associated with
a communicator.
#include <mpi.h>
int MPI_Comm_size(MPI_Comm comm, int *size)
USE MPI
! or the older form: INCLUDE ’mpif.h’
MPI_COMM_SIZE(COMM, SIZE, IERROR)
INTEGER COMM, SIZE, IERROR
USE mpi_f08
MPI_Comm_size(comm, size, ierror)
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, INTENT(OUT) :: size
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
- comm
- Communicator (handle).
- size
- Number
of processes in the group of comm (integer).
- IERROR
- Fortran only: Error
status (integer).
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.
MPI_COMM_NULL is not considered a valid
argument to this function.
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.
MPI_Comm_group
MPI_Comm_rank
MPI_Comm_compare
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