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NAME

MPI_Comm_compare - Compares two communicators

SYNOPSIS

#include <mpi.h> int MPI_Comm_compare(MPI_Comm c1 , MPI_Comm c2 , int *result );

#include <pmpi.h> int PMPI_Comm_compare(MPI_Comm c1 , MPI_Comm c2 , int *result );

#include <mpi.h> static int MPI::Comm::Compare(const Comm &c1 , const Comm &c2 );

INCLUDE 'mpif.h' MPI_COMM_COMPARE(c1 , c2 , result , ierr ) INTEGER c1 , c2 , result , ierr

INPUT PARAMETERS

c1 - communicator (handle)

c2 - communicator (handle)

OUTPUT PARAMETER

result - the result of the comparison (integer).

DESCRIPTION

The MPI_Comm_compare() function is used to compare two communicators c1 and c2 . If the two communicators are identical, then MPI_IDENT is returned in result . If they are not identical, then internally, the output of a call to the MPI_Group_compare() function is used to compare the groups that make up the communicators. If the groups that compose the communicators are different, then MPI_UNEQUAL is returned. If the groups are similar then MPI_SIMILAR is returned. Otherwise MPI_CONGRUENT is returned in result .

In C++, the result of the comparison is the return value.

Note that the communicators must be valid (not MPI_COMM_NULL). PMPI_Comm_compare() is the profiling version of this function.

ERRORS

All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.

In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.

MPI_SUCCESS - No error;

MPI_ERR_PENDING - Pending exception;

MPI_ERR_COMM - Invalid communicator;

MPI_ERR_ARG - Invalid output pointer.

SEE ALSO

MPI_Group_compare (3) MPI_Comm_create (3) MPI_Comm_free (3) MPI_Intercomm_create (3)

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