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SYNTAX
C Syntax
#include <mpi.h>
int MPI_Intercomm_create_from_groups(MPI_Group local_group, int local_leader, MPI_Group remote_group, int remote_leader, const char *stringtag, MPI_Info info, MPI_Errhandler errhandler, MPI_Comm *newintercomm)
Fortran Syntax
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_INTERCOMM_CREATE_FROM_GROUPS(LOCAL_GROUP, LOCAL_LEADER, REMOTE_GROUP, REMOTE_LEADER, STRINGTAG, INFO, ERRHANDLER, NEWINTERCOMM, IERROR)
INTEGER LOCAL_GROUP, LOCAL_LEADER, REMOTE_GROUP, REMOTE_LEADER, INFO, ERRHANDLER, NEWINTERCOMM, IERROR
CHARACTER*(*) STRINGTAG
Fortran 2008 Syntax
USE mpi_f08
MPI_Intercomm_create_from_groups(local_group, local_leader, remote_group, remote_leader, stringtag, info, errhandler, newintercomm, ierror)
TYPE(MPI_Group), INTENT(IN) :: local_group, remote_group
INTEGER, INTENT(IN) :: local_leader, remote_leader
CHARACTER(LEN=*), INTENT(IN) :: stringtag
TYPE(MPI_Info), INTENT(IN) :: info
TYPE(MPI_Errhandler), INTENT(IN) :: errhandler
TYPE(MPI_Comm), INTENT(OUT) :: newintercomm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
INPUT PARAMETERS
• local_group : Local group (handler)
• local_leader : rank of local group leader in local_group (integer)
• remote_group : Remote group (handler)
•
remote_leader (rank of remote leader in remote_group, significant)
only at local_leader (integer)
• stringtag : Unique identifier for this operation (string)
• info : info object (handler)
•
errhandler (error handler to be attached to the new)
inter-communicator (handle)
OUTPUT PARAMETERS
• newintercomm : New inter-communicator (handle).
• ierror : Fortran only: Error status (integer).
DESCRIPTION
MPI_Intercomm_create_from_groups creates an inter-communicator. Unlike MPI_Intercomm_create, this
function uses as input previously defined, disjoint local and remote groups. The calling MPI process must
be a member of the local group. The call is collective over the union of the local and remote groups. All
involved MPI processes shall provide an identical value for the stringtag argument. Within each group,
all MPI processes shall provide identical local_group, local_leader arguments. Wildcards are not
permitted for the remote_leader or local_leader arguments. The stringtag argument serves the same purpose
as the stringtag used in the MPI_Comm_create_from_group function; it differentiates concurrent calls in a
multithreaded environment. The stringtag shall not exceed MPI_MAX_STRINGTAG_LEN characters in length.
For C, this includes space for a null terminating character. In the event that MPI_GROUP_EMPTY is
supplied as the local_group or remote_group1 or both, then the call is a local operation and
MPI_COMM_NULL is returned as the newintercomm.
NOTES
The errhandler argument specifies an error handler to be attached to the new inter-communicator. The info
argument provides hints and assertions, possibly MPI implementation dependent, which indicate desired
characteristics and guide communicator creation. MPI_MAX_STRINGTAG_LEN shall have a value of at least 63.
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_Comm_create_from_group
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Feb 17, 2025 MPI_INTERCOMM_CREATE_FROM_GROUPS(3)