.TH MPI_Comm_size 3 "11/12/2019" " " "MPI"
.SH NAME
MPI_Comm_size \-  Determines the size of the group associated with a communicator 
.SH SYNOPSIS
.nf
int MPI_Comm_size(MPI_Comm comm, int *size)
.fi
.SH INPUT PARAMETERS
.PD 0
.TP
.B comm 
- communicator (handle)
.PD 1

.SH OUTPUT PARAMETERS
.PD 0
.TP
.B size 
- number of processes in the group of 
.I comm
(integer)
.PD 1

.SH NOTES

.SH 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:
.nf
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.
.fi


.SH 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.

.SH NOTES FOR FORTRAN
All MPI routines in Fortran (except for 
.I MPI_WTIME
and 
.I MPI_WTICK
) have
an additional argument 
.I ierr
at the end of the argument list.  
.I 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
.I call
statement.

All MPI objects (e.g., 
.I MPI_Datatype
, 
.I MPI_Comm
) are of type 
.I INTEGER
in Fortran.

.SH ERRORS

All MPI routines (except 
.I MPI_Wtime
and 
.I 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 
.I MPI_Comm_set_errhandler
(for communicators),
.I MPI_File_set_errhandler
(for files), and 
.I MPI_Win_set_errhandler
(for
RMA windows).  The MPI-1 routine 
.I MPI_Errhandler_set
may be used but
its use is deprecated.  The predefined error handler
.I MPI_ERRORS_RETURN
may be used to cause error values to be returned.
Note that MPI does 
.B not
guarentee that an MPI program can continue past
an error; however, MPI implementations will attempt to continue whenever
possible.

.PD 0
.TP
.B MPI_SUCCESS 
- No error; MPI routine completed successfully.
.PD 1
.PD 0
.TP
.B MPI_ERR_COMM 
- Invalid communicator.  A common error is to use a null
communicator in a call (not even allowed in 
.I MPI_Comm_rank
).
.PD 1
.PD 0
.TP
.B MPI_ERR_ARG 
- Invalid argument.  Some argument is invalid and is not
identified by a specific error class (e.g., 
.I MPI_ERR_RANK
).
.PD 1