.\" -*- nroff -*-
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" Copyright (c) 2020      Google, LLC. All rights reserved.
.\" $COPYRIGHT$
.TH MPI_Comm_compare 3 "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
.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 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.
.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.