MPI_CART_COORDS(3)

💖 MPI_CART_COORDS(3) 💖

okay bestie, sit down, hydrate, and let me tell you about MPI_Cart_coords — page three of the Open MPI manual, and honestly? iconic. 💅 This is where you find out who a process is in your Cartesian topology. Not a vibe check, an actual coordinates check. ✨

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🎀 NAME 🎀

MPI_Cart_coords — determines process coords in Cartesian topology given rank in group. fr fr that's the whole job. 🫶

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🌈 SYNTAX 🌈

✨ C Syntax ✨

#include <mpi.h>

int MPI_Cart_coords(MPI_Comm comm, int rank, int maxdims,
    int coords[])

✨ Fortran Syntax ✨

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

MPI_CART_COORDS(COMM, RANK, MAXDIMS, COORDS, IERROR)
    INTEGER COMM, RANK, MAXDIMS, COORDS(*), IERROR

✨ Fortran 2008 Syntax ✨

USE mpi_f08

MPI_Cart_coords(comm, rank, maxdims, coords, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: comm
    INTEGER, INTENT(IN) :: rank, maxdims
    INTEGER, INTENT(OUT) :: coords(maxdims)
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🌸 INPUT PARAMETERS 🌸

• comm — the communicator with Cartesian structure (handle). it's giving "the shape of the world you live in" 🗺️
• rank — rank of a process within group of comm (integer). yes, that rank, the one you already know.
• maxdims — (Length of vector coords in the calling program) (integer). Length of vector coords in the calling program (integer). no cap, that's the parameter description, and it's the length of coords in the calling program. 🎀

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🦋 OUTPUT PARAMETERS 🦋

• coords — integer array (of size ndims, which was defined by the MPI_Cart_create call) containing the Cartesian coordinates of specified process (integer). this is the whole point bestie, this is your address 🌟
• ierror — Fortran only: error status (integer).

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💜 DESCRIPTION 💜

MPI_Cart_coords provides a mapping of ranks to Cartesian coordinates. that's it. that's the function. you hand it a rank, it hands you back where in the grid that process lives. lowkey magical, highkey just arithmetic, and we love her for it. 🔥

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💀 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. yes literally all of them, so pay attention. 😭

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. it's giving no survivors, not a drill 💀
• 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. the chill one, she just tells you and moves on 🫶

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. not a joke, not a vibe, an actual caveat bestie. 😳

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.

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🫶 COPYRIGHT 🫶

2003-2026, The Open MPI Community

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okay that's the whole page, you ate that. 💖 this was MPI_CART_COORDS(3) from the Open MPI manual, version marked Sep 10, 2026 — go call her on some Cartesian grid and tell her I said hi. mwah. 💅✨🎀🦋🌸