.\" -*- nroff -*-
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Comm_compare 3 "May 26, 2022" "4.1.4" "Open MPI"
.SH NAME
\fBMPI_Comm_compare \fP \-  Compares two communicators.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Comm_compare(MPI_Comm \fIcomm1\fP, MPI_Comm\fI comm2\fP, int\fI *result\fP)

.fi
.SH Fortran Syntax
.nf
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_COMM_COMPARE(\fICOMM1, COMM2, RESULT, IERROR\fP)
	INTEGER	\fICOMM1, COMM2, RESULT, IERROR\fP

.fi
.SH Fortran 2008 Syntax
.nf
USE mpi_f08
MPI_Comm_compare(\fIcomm1\fP, \fIcomm2\fP, \fIresult\fP, \fIierror\fP)
	TYPE(MPI_Comm), INTENT(IN) :: \fIcomm1\fP, \fIcomm2\fP
	INTEGER, INTENT(OUT) :: \fIresult\fP
	INTEGER, OPTIONAL, INTENT(OUT) :: \fIierror\fP

.fi
.SH C++ Syntax
.nf
#include <mpi.h>
static int Comm::Compare(const Comm& \fIcomm1\fP, const Comm& \fIcomm2\fP)

.fi
.SH INPUT PARAMETERS
.ft R
.TP 1i
comm1
Comm1 (handle).
.TP 1i
comm2
Comm2 (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
result
Result of comparison (integer).
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
MPI_IDENT results if and only if comm1 and comm2 are handles for the same object (identical groups and same contexts). MPI_CONGRUENT results if the underlying groups are identical in constituents and rank order; these communicators differ only by context. MPI_SIMILAR results of the group members of both communicators are the same but the rank order differs. MPI_UNEQUAL results otherwise.

.SH 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++ 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.
.sp
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.