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.TH "MPI_GRAPH_GET" "3" "Jul 22, 2024" "" "Open MPI"
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\fI\%MPI_Graph_get\fP — Retrieves graph topology information associated with a
communicator.
.SH SYNTAX
.SS C Syntax
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.INDENT 3.5
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.nf
.ft C
#include <mpi.h>

int MPI_Graph_get(MPI_Comm comm, int maxindex, int maxedges,
    int index[], int edges[])
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.SS Fortran Syntax
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.INDENT 3.5
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.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq

MPI_GRAPH_GET(COMM, MAXINDEX, MAXEDGES, INDEX, EDGES, IERROR)
    INTEGER COMM, MAXINDEX, MAXEDGES, INDEX(*)
    INTEGER EDGES(*), IERROR
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.SS Fortran 2008 Syntax
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.ft C
USE mpi_f08

MPI_Graph_get(comm, maxindex, maxedges, index, edges, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: comm
    INTEGER, INTENT(IN) :: maxindex, maxedges
    INTEGER, INTENT(OUT) :: index(maxindex), edges(maxedges)
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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.SH INPUT PARAMETERS
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.IP \(bu 2
\fBcomm\fP : Communicator with graph structure (handle).
.IP \(bu 2
\fBmaxindex\fP : Length of vector index in the calling program (integer).
.IP \(bu 2
\fBmaxedges\fP : Length of vector edges in the calling program (integer).
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.SH OUTPUT PARAMETERS
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.IP \(bu 2
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.TP
.B \fBindex\fP
Array of integers containing the graph structure (for details
see the definition of MPI_Graph_create).
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.IP \(bu 2
\fBedges\fP : Array of integers containing the graph structure.
.IP \(bu 2
\fBierror\fP : Fortran only: Error status (integer).
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.SH DESCRIPTION
.sp
Functions \fI\%MPI_Graphdims_get\fP and \fI\%MPI_Graph_get\fP retrieve the
graph\-topology information that was associated with a communicator by
\fI\%MPI_Graph_create\fP\&.
.sp
The information provided by \fI\%MPI_Graphdims_get\fP can be used to dimension
the vectors index and edges correctly for a call to \fI\%MPI_Graph_get\fP\&.
.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.
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Open MPI includes three predefined error handlers that can be used:
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.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.
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MPI applications can also implement their own error handlers by calling:
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.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
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Note that MPI does not guarantee that an MPI program can continue past
an error.
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See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
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See the Error Handling section of the MPI\-3.1 standard for
more information.
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\fBSEE ALSO:\fP
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.INDENT 3.5
\fI\%MPI_Graph_create\fP
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.SH COPYRIGHT
2003-2024, The Open MPI Community
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