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.\" Man page generated from reStructuredText.
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.TH "MPI_COMM_CREATE_FROM_GROUP" "3" "May 30, 2025" "" "Open MPI"
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.sp
\fI\%MPI_Comm_create_from_group\fP — Creates a new communicator from a group and
stringtag
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#include <mpi.h>
int MPI_Comm_create_from_group(MPI_Group group, const char *stringtag, MPI_Info info, MPI_Errhandler errhandler, MPI_Comm *newcomm)
.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_COMM_CREATE_FROM_GROUP(GROUP, STRINGTAG, INFO, ERRHANDLER, NEWCOMM, IERROR)
INTEGER GROUP, INFO, ERRHANDLER, NEWCOMM, 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_Comm_create_from_group(group, stringtag, info, errhandler, newcomm, ierror)
TYPE(MPI_Group), INTENT(IN) :: group
CHARACTER(LEN=*), INTENT(IN) :: stringtag
TYPE(MPI_Info), INTENT(IN) :: info
TYPE(MPI_Errhandler), INTENT(IN) :: errhandler
TYPE(MPI_Comm), INTENT(OUT) :: newcomm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
.ft P
.fi
.UNINDENT
.UNINDENT
.SH INPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBgroup\fP : Group (handler)
.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
intra\-communicator (handle)
.UNINDENT
.UNINDENT
.SH OUTPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBnewcomm\fP : New communicator (handle).
.IP \(bu 2
\fBierror\fP : Fortran only: Error status (integer).
.UNINDENT
.SH DESCRIPTION
.sp
\fI\%MPI_Comm_create_from_group\fP is similar to \fI\%MPI_Comm_create_group\fP, except
that the set of MPI processes involved in the creation of the new
intra\-communicator is specified by a group argument, rather than the
group associated with a pre\-existing communicator. If a non\-empty group
is specified, then all MPI processes in that group must call the
function and each of these MPI processes must provide the same
arguments, including a group that contains the same members with the
same ordering, and identical stringtag value. In the event that
MPI_GROUP_EMPTY is supplied as the group argument, then the call is a
local operation and MPI_COMM_NULL is returned as newcomm. The stringtag
argument is analogous to the tag used for \fI\%MPI_Comm_create_group\fP\&. If
multiple threads at a given MPI process perform concurrent
\fI\%MPI_Comm_create_from_group\fP operations, the user must distinguish these
operations by providing different stringtag arguments. The stringtag
shall not exceed MPI_MAX_STRINGTAG_LEN characters in length. For C, this
includes space for a null terminating character.
.SH NOTES
.sp
The errhandler argument specifies an error handler to be attached to the
new intracommunicator. 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
.INDENT 0.0
.IP \(bu 2
\fI\%MPI_Comm_create_group\fP
.UNINDENT
.UNINDENT
.UNINDENT
.SH COPYRIGHT
2003-2025, The Open MPI Community
.\" Generated by docutils manpage writer.
.
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