MPI_CART_GET(3)

💖 MPI_CART_GET(3) 💖

okay so bestie, welcome to the Open MPI manual page for MPI_Cart_get — that's the MPI_CART_GET(3) entry, and no, you're not lost, this is exactly where you're supposed to be 🫶

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✨ NAME ✨

MPI_Cart_get — Retrieves Cartesian topology information associated with a communicator. it's giving "tell me everything about my little grid" energy 👑

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✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

int MPI_Cart_get(MPI_Comm comm, int maxdims, int dims[], int periods[],
    int coords[])

🌸 Fortran Syntax

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

MPI_CART_GET(COMM, MAXDIMS, DIMS, PERIODS, COORDS, IERROR)
    INTEGER COMM, MAXDIMS, DIMS(*), COORDS(*), IERROR
    LOGICAL PERIODS(*)

🌸 Fortran 2008 Syntax

USE mpi_f08

MPI_Cart_get(comm, maxdims, dims, periods, coords, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: comm
    INTEGER, INTENT(IN) :: maxdims
    INTEGER, INTENT(OUT) :: dims(maxdims), coords(maxdims)
    LOGICAL, INTENT(OUT) :: periods(maxdims)
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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✨ INPUT PARAMETERS ✨

• comm — Communicator with Cartesian structure (handle). this is the friend you're asking about 💖
• maxdims — Length of vectors dims, periods, and coords in the calling program (integer). 🌈

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✨ OUTPUT PARAMETERS ✨

• dims — Number of processes for each Cartesian dimension (array of integers). ⭐
• periods — Periodicity (true/false) for each Cartesian dimension (array of logicals). 🔁
• coords — Coordinates of calling process in Cartesian structure (array of integers). 📍
• ierror — Fortran only: Error status (integer).

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✨ DESCRIPTION ✨

so the functions MPI_Cartdim_get and MPI_Cart_get return the Cartesian topology information that was associated with a communicator by MPI_Cart_create. that's it, that's the vibe — you made the grid with MPI_Cart_create, and now you're asking it to spill the tea about itself 🎀

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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. 💅

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_Cartdim_get

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✨ Copyright ✨

2003-2026, The Open MPI Community

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and that's the whole page, bestie!! 🦋 this was Sep 10, 2026 — the day this manual page said what it said, and also the day you finally understood Cartesian topologies. iconic behavior, honestly. go call MPI_Cart_get and slay 💜 👑 ✨