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.\" Man page generated from reStructuredText.
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.TH "MPI_INTERCOMM_CREATE_FROM_GROUPS" "3" "May 30, 2025" "" "Open MPI"
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.sp
\fI\%MPI_Intercomm_create_from_groups\fP — Creates a new inter\-communicator from
a local and remote group and stringtag
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#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)
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq
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
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran 2008 Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
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
.ft P
.fi
.UNINDENT
.UNINDENT
.SH INPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBlocal_group\fP : Local group (handler)
.IP \(bu 2
\fBlocal_leader\fP : rank of local group leader in local_group (integer)
.IP \(bu 2
\fBremote_group\fP : Remote group (handler)
.IP \(bu 2
.INDENT 2.0
.TP
.B \fBremote_leader\fP
rank of remote leader in remote_group, significant
only at local_leader (integer)
.UNINDENT
.IP \(bu 2
\fBstringtag\fP : Unique identifier for this operation (string)
.IP \(bu 2
\fBinfo\fP : info object (handler)
.IP \(bu 2
.INDENT 2.0
.TP
.B \fBerrhandler\fP
error handler to be attached to the new
inter\-communicator (handle)
.UNINDENT
.UNINDENT
.SH OUTPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBnewintercomm\fP : New inter\-communicator (handle).
.IP \(bu 2
\fBierror\fP : Fortran only: Error status (integer).
.UNINDENT
.SH DESCRIPTION
.sp
\fI\%MPI_Intercomm_create_from_groups\fP creates an inter\-communicator. Unlike
\fI\%MPI_Intercomm_create\fP, 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 \fI\%MPI_Comm_create_from_group\fP 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.
.SH NOTES
.sp
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.
.SH ERRORS
.sp
Almost all MPI routines return an error value; C routines as the return result
of the function and Fortran routines in the last argument.
.sp
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
\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
Model exclusively) the error raises the initial error handler. The initial
error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
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.
.sp
Open MPI includes three predefined error handlers that can be used:
.INDENT 0.0
.IP \(bu 2
\fBMPI_ERRORS_ARE_FATAL\fP
Causes the program to abort all connected MPI processes.
.IP \(bu 2
\fBMPI_ERRORS_ABORT\fP
An error handler that can be invoked on a communicator,
window, file, or session. When called on a communicator, it
acts as if \fI\%MPI_Abort\fP was called on that communicator. If
called on a window or file, acts as if \fI\%MPI_Abort\fP 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.
.IP \(bu 2
\fBMPI_ERRORS_RETURN\fP
Returns an error code to the application.
.UNINDENT
.sp
MPI applications can also implement their own error handlers by calling:
.INDENT 0.0
.IP \(bu 2
\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
.IP \(bu 2
\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
.UNINDENT
.sp
Note that MPI does not guarantee that an MPI program can continue past
an error.
.sp
See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
.sp
See the Error Handling section of the MPI\-3.1 standard for
more information.
.sp
\fBSEE ALSO:\fP
.INDENT 0.0
.INDENT 3.5
\fI\%MPI_Comm_create_from_group\fP
.UNINDENT
.UNINDENT
.SH COPYRIGHT
2003-2025, The Open MPI Community
.\" Generated by docutils manpage writer.
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