plucky (3) MPI_Intercomm_merge.openmpi.3.gz
SYNTAX
C Syntax
#include <mpi.h>
int MPI_Intercomm_merge(MPI_Comm intercomm, int high,
MPI_Comm *newintracomm)
Fortran Syntax
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_INTERCOMM_MERGE(INTERCOMM, HIGH, NEWINTRACOMM, IERROR)
INTEGER INTERCOMM, NEWINTRACOMM, IERROR
LOGICAL HIGH
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
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).
OUTPUT PARAMETERS
• newintracomm: Created intracommunicator (type indicator).
• ierror: Fortran only: Error status (integer).
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.
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/‐
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.
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 by calling:
• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler
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-3.1 standard for more information.
SEE ALSO:
• MPI_Intercomm_create
• MPI_Comm_free
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2003-2025, The Open MPI Community
Feb 17, 2025 MPI_INTERCOMM_MERGE(3)