18.2.235. MPI_Intercomm_merge

MPI_Intercomm_merge - Creates an intracommunicator from an intercommunicator.

18.2.235.1. SYNTAX

18.2.235.1.1. C Syntax

#include <mpi.h>

int MPI_Intercomm_merge(MPI_Comm intercomm, int high,
     MPI_Comm *newintracomm)

18.2.235.1.2. Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_INTERCOMM_MERGE(INTERCOMM, HIGH, NEWINTRACOMM, IERROR)
     INTEGER INTERCOMM, NEWINTRACOMM, IERROR
     LOGICAL HIGH

18.2.235.1.3. Fortran 2008 Syntax

USE mpi_f08
MPI_Intercomm_merge(intercomm, high, newintracomm, ierror)
     TYPE(MPI_Comm), INTENT(IN) :: intercomm
     LOGICAL, INTENT(IN) :: high
     TYPE(MPI_Comm), INTENT(OUT) :: newintracomm
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

18.2.235.2. INPUT PARAMETERS

  • intercomm: Intercommunicator (type indicator).

  • high: Used to order the groups of the two intracommunicators within comm when creating the new communicator (type indicator).

18.2.235.3. OUTPUT PARAMETERS

  • newintracomm: Created intracommunicator (type indicator).

  • IERROR: Fortran only: Error status (integer).

18.2.235.4. DESCRIPTION

This function creates an intracommunicator from the union of the two groups that are associated with intercomm. All processes should provide the same high value within each of the two groups. If processes in one group provide the value high = false and processes in the other group provide the value high = true, then the union orders the “low” group before the “high” group. If all processes provide the same high argument, then the order of the union is arbitrary. This call is blocking and collective within the union of the two groups.

18.2.235.5. ERRORS

Almost all MPI routines return an error value; C routines as the return result of the function and Fortran routines in the last argument.

Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_INIT / MPI_INIT_THREAD, after MPI_FINALIZE, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI_COMM_SET_ERRHANDLER on MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_COMM_SPAWN[_MULTIPLE]. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all other MPI functions.

In the sessions model, the error handler can be set during MPI_Session_init.

Open MPI includes three predefined error handlers that can be used:

MPI_ERRORS_ARE_FATAL: Causes the program to abort all connected MPI processes.
MPI_ERRORS_ABORT:     An error handler that can be invoked on a communicator,
                      window, file, or session. When called on a communicator, it
                      acts as if MPI_ABORT was called on that communicator. If
                      called on a window or file, acts as if MPI_ABORT was called
                      on a communicator containing the group of processes in the
                      corresponding window or file. If called on a session,
                      aborts only the local process.
MPI_ERRORS_RETURN:    Returns an error code to the application.

MPI applications can also implement their own error handlers.

Custom MPI error handlers can be created by calling: MPI_Comm_create_errhandler(3) MPI_File_create_errhandler(3) MPI_Session_create_errhandler(3) MPI_Win_create_errhandler(3)

Predefined and custom error handlers can be set by calling: MPI_Comm_set_errhandler(3) MPI_File_set_errhandler(3) MPI_Session_set_errhandler(3) MPI_Win_set_errhandler(3)

Note that MPI does not guarantee that an MPI program can continue past an error.

See the MPI man page for a full list of MPI error codes.

See the Error Handling section of the MPI-3 standard for more information.