MPI_OP_COMMUTATIVE(3)

💖 MPI_OP_COMMUTATIVE 💖

okay bestie, welcome to the Open MPI manual, page MPI_OP_COMMUTATIVE(3) — yes the third section, we're in library-call territory, very demure, very mindful 🎀

✨ NAME ✨

MPI_Op_commutative — bestie, this is literally just a vibe check for your reduction operation. You're asking: is this op commutative or not? That's it. That's the whole function. 🦋

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✨ SYNTAX ✨

💅 C Syntax

#include <mpi.h>

int MPI_Op_commutative(MPI_Op op, int *commute)

💅 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_OP_COMMUTATIVE(OP, COMMUTE, IERROR)
     LOGICAL COMMUTE
     INTEGER OP, IERROR

💅 Fortran 2008 Syntax

USE mpi_f08
MPI_Op_commutative(op, commute, ierror)
     TYPE(MPI_Op), INTENT(IN) :: op
     INTEGER, INTENT(OUT) :: commute
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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✨ INPUT PARAMETER ✨

• op — the operation, as a handle. That's the thing you're interrogating. 👑

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✨ OUTPUT PARAMETERS ✨

• commute — true if op is commutative, false if it's not. Logical, periodt. 💖
• ierror — Fortran only, babes: the error status, an integer. 🙈

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✨ DESCRIPTION ✨

Reduction operations can be queried for their commutativity. That's the plot. You hand over an op, it tells you whether it commutes. slay 🌈

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✨ ERRORS ✨

ngl, here's where it gets real — almost every MPI routine gives you back an error value. C routines? That's the return result of the function. Fortran routines? It's the last argument. 🌸

Before the error value comes back to you, the current MPI error handler that's attached to the communication object (think: communicator, window, file) gets called. And if no communication object is tied to the MPI call at all, then the call is considered attached to MPI_COMM_SELF and it'll call the error handler associated with that. Now — when MPI_COMM_SELF is not initialized (aka before MPI_Init / MPI_Init_thread, after MPI_Finalize, or when you're using the Sessions Model exclusively), the error raises the initial error handler instead. You can swap out that initial error handler by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when you're in the World model, or via the mpi_initial_errhandler CLI argument to mpiexec, or with the info key to MPI_Comm_spawn / MPI_Comm_spawn_multiple. And if literally no other appropriate error handler has been set? Then the MPI_ERRORS_RETURN handler gets called for MPI I/O functions, and MPI_ERRORS_ABORT gets called for all the other MPI functions. 😭

Open MPI ships three predefined error handlers you can use:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. yeah. everyone. 💀
• MPI_ERRORS_ABORT — an error handler you can invoke on a communicator, window, file, or session. Called on a communicator, it acts as if MPI_Abort was called on that communicator. 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. Called on a session, it aborts only the local process.
• MPI_ERRORS_RETURN — returns an error code back to your application. chill of it honestly. 🫶

Your MPI application can also implement its own error handlers by calling:

• MPI_Comm_create_errhandler and then MPI_Comm_set_errhandler
• MPI_File_create_errhandler and then MPI_File_set_errhandler
• MPI_Session_create_errhandler and then MPI_Session_set_errhandler, or at MPI_Session_init
• MPI_Win_create_errhandler and then MPI_Win_set_errhandler

⚠️ Heads up bestie: note that MPI does not guarantee that an MPI program can continue past an error. Like, at all. Do not make plans after this 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_Op_create

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✨ Copyright ✨

2003-2026, The Open MPI Community

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and that's the whole page, no cap 💜 thanks for reading my little manual moment — this was the Open MPI MPI_OP_COMMUTATIVE(3) page, version dated Sep 10, 2026, footer and all, and you ate it up fr fr ✨🎀🦋