MPI_GRAPH_MAP(3)

💅 MPI_GRAPH_MAP(3) — like, the Open MPI girlie edition 🎀

okay so bestie, this is the MPI_Graph_map page from Open MPI — it's the function that maps process to graph topology information. Yes queen, topology. Let's get into it ✨

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✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

int MPI_Graph_map(MPI_Comm comm, int nnodes, const int index[],
    const int edges[], int *newrank)

🌸 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_GRAPH_MAP(COMM, NNODES, INDEX, EDGES, NEWRANK, IERROR)
    INTEGER COMM, NNODES, INDEX(*), EDGES(*), NEWRANK, IERROR

🌸 Fortran 2008 Syntax

USE mpi_f08

MPI_Graph_map(comm, nnodes, index, edges, newrank, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: comm
    INTEGER, INTENT(IN) :: nnodes, index(nnodes), edges(*)
    INTEGER, INTENT(OUT) :: newrank
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🫶 INPUT PARAMETERS

• comm — the input communicator, it's a handle, slay 💅
• nnodes — number of graph nodes, an integer, no cap
• index — integer array that specifies the graph structure — like, go read MPI_Graph_create for the deets, iykyk 🦋
• edges — integer array that also specifies the graph structure, bestie 🌈

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👑 OUTPUT PARAMETERS

• newrank — the reordered rank of the calling process, an integer 💖 — and it's MPI_UNDEFINED if the calling process does not belong to the graph, so watch out for that one 🙈
• ierror — Fortran only: the error status (integer) ⭐

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🧚 DESCRIPTION 🧚

so MPI_Cart_map and MPI_Graph_map can be used to implement, like, all the other topology functions — main character energy fr. In general they won't be called by the user directly, unless they're out here creating additional virtual topology capability other than that provided by MPI. periodt. ✨

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💀 ERRORS 💀

okay so almost all MPI routines return an error value — C routines as the return result of the function, and Fortran routines in the last argument. noted. 🫶

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, and honestly, iconic lineup:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. dramatic but valid 💀
• 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, it 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, it aborts only the local process. multi-talented fr 🔥
• MPI_ERRORS_RETURN — returns an error code to the application. the chill one 🌸

MPI applications can also implement their own error handlers by calling, bestie take notes:

• 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. so like, don't count on it 🙈

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. iykyk 📚

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🦋 SEE ALSO

• MPI_Cart_map — the other map function, go say hi 💜

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🎀 COPYRIGHT

2003-2026, The Open MPI Community

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and that's the whole page bestie!! 💖 this was MPI_GRAPH_MAP(3) from the Open MPI manual, dated Sep 11, 2026 — go forth and map those graphs, you absolute icon 👑✨