MPI\_INTERCOMM\_CREATE\_FROM\_GROUPS(3) Open MPI MPI\_INTERCOMM\_CREATE\_FROM\_GROUPS(3) MPI\_Intercomm\_create\_from\_groups — Creates a new inter-communicator from a local and remote group and stringtag # [SYNTAX](#SYNTAX) ## [C Syntax](#C_Syntax) ``` #include 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](#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](#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](#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)**](#remote_leader) 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)**](#errhandler) inter-communicator (handle) # [OUTPUT PARAMETERS](#OUTPUT_PARAMETERS) - **newintercomm** : New inter-communicator (handle). - **ierror** : Fortran only: Error status (integer). # [DESCRIPTION](#DESCRIPTION) MPI\_Intercomm\_create\_from\_groups creates an inter-communicator. Unlike MPI\_Intercomm\_create <#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 <#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](#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](#ERRORS) [Important](#Important) In Open MPI, this function only works properly when the MPI job is launched via mpirun / mpiexec <#man1-mpirun>. Using this function in other run-time environments is currently unsupported, and may result in undefined behavior (e.g., the MPI job may hang). 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>/MPI\_Init\_thread <#mpi-init-thread>, after MPI\_Finalize <#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 <#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>/MPI\_Comm\_spawn\_multiple <#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 <#mpi-abort> was called on that communicator. If called on a window or file, acts as if MPI\_Abort <#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 <#mpi-comm-create-errhandler> then MPI\_Comm\_set\_errhandler <#mpi-comm-set-errhandler> - MPI\_File\_create\_errhandler <#mpi-file-create-errhandler> then MPI\_File\_set\_errhandler <#mpi-file-set-errhandler> - MPI\_Session\_create\_errhandler <#mpi-session-create-errhandler> then MPI\_Session\_set\_errhandler <#mpi-session-set-errhandler> or at MPI\_Session\_init <#mpi-session-init> - MPI\_Win\_create\_errhandler <#mpi-win-create-errhandler> then MPI\_Win\_set\_errhandler <#mpi-win-set-errhandler> Note that MPI does not guarantee that an MPI program can continue past an error. See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>. See the Error Handling section of the MPI-3.1 standard for more information. **See also:** MPI\_Comm\_create\_from\_group <#mpi-comm-create-from-group> # [Copyright](#Copyright) 2003-2026, The Open MPI Community November 1, 2026 --- Document: MPI_Intercomm_create_from_groups(3) from openmpi-cuda-12.9 5.0.11-r1 (Chainguard OS) Source: https://github.com/open-mpi/ompi