MPI_CART_COORDS(3)

💅 MPI_CART_COORDS ✨

okay so this is the MPI_Cart_coords page from the Open MPI manual, and bestie, it's literally the "rank → coordinates" glow-up function. Let's get into it 🫶

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🌸 NAME 🌸

MPI_Cart_coords — determines process coords in Cartesian topology given rank in group.

Like, you hand it a rank and it tells you where that process actually lives in the grid. main character energy fr fr ✨

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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 — communicator with Cartesian structure (handle). this is the one that's gotta have the grid vibe already set up 💅
• rank — rank of a process within group of comm (integer). the number you're asking about 👑
• maxdims — length of vector coords in the calling program (integer). length of vector coords in the calling program (integer). (yes bestie it's listed twice in the original — we love a repeat legend 🙈)

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🌈 OUTPUT PARAMETERS 🌈

• coords — integer array (of size ndims, which was defined by MPI_Cart_create call) containing the Cartesian coordinates of specified process (integer). this is where the answer lands, queen 🎯
• 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 whole thing. you give rank, you get coords. slay, honestly 🧚

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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. no cap.

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. dramatic? yes. effective? also yes 💀
• 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 🫶

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. like, it might just be over. protect your peace 🥲

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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and that's the whole page, bestie — go map some ranks 💜

MPI_CART_COORDS(3) — from Open MPI, dated Sep 11, 2026 🌸✨

okay ily, go touch some Cartesian product grids 🦋🎀