---
name: "MPI_Graph_get.openmpi"
section: "3"
platform: "linux"
package: "openmpi-doc"
version: "5.0.7-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/MPI_Graph_get.openmpi"
---

# MPI\_Graph\_get.openmpi(3)

*MPI\_Graph\_get* — Retrieves graph topology information associated with a communicator.

## SYNTAX

### C Syntax

```
#include <mpi.h>
int MPI_Graph_get(MPI_Comm comm, int maxindex, int maxedges,
    int index[], int edges[])
```

### Fortran Syntax

```
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_GRAPH_GET(COMM, MAXINDEX, MAXEDGES, INDEX, EDGES, IERROR)
    INTEGER COMM, MAXINDEX, MAXEDGES, INDEX(*)
    INTEGER EDGES(*), IERROR
```

### Fortran 2008 Syntax

```
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
```

## INPUT PARAMETERS

- •

  **comm** : Communicator with graph structure (handle).

- •

  **maxindex** : Length of vector index in the calling program (integer).

- •

  **maxedges** : Length of vector edges in the calling program (integer).

## OUTPUT PARAMETERS

- •

  - **index (Array of integers containing the graph structure (for details)**

    see the definition of MPI\_Graph\_create).

- •

  **edges** : Array of integers containing the graph structure.

- •

  **ierror** : Fortran only: Error status (integer).

## DESCRIPTION

Functions *MPI\_Graphdims\_get* and *MPI\_Graph\_get* retrieve the graph-topology information that was associated with a communicator by *MPI\_Graph\_create*.

The information provided by *MPI\_Graphdims\_get* can be used to dimension the vectors index and edges correctly for a call to *MPI\_Graph\_get*.

## 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\_Graph\_create*

## COPYRIGHT

2003-2025, The Open MPI Community