MPI_GROUP_COMPARE(3)

💅 NAME

MPI_Group_compare — compares two groups, bestie. That's it. That's the whole job. 🫶

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✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

int MPI_Group_compare(MPI_Group group1, MPI_Group group2,
    int *result)

🎀 Fortran Syntax

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

MPI_GROUP_COMPARE(GROUP1, GROUP2, RESULT, IERROR)
    INTEGER GROUP1, GROUP2, RESULT, IERROR

🦋 Fortran 2008 Syntax

USE mpi_f08

MPI_Group_compare(group1, group2, result, ierror)
    TYPE(MPI_Group), INTENT(IN) :: group1, group2
    INTEGER, INTENT(OUT) :: result
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🌈 INPUT PARAMETERS

• _group1_ — the first group, as a handle. 🎀
• _group2_ — the second group, also a handle. 💖

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👑 OUTPUT PARAMETERS

• _result_ — an integer, and honestly it's giving three possible moods: MPI_IDENT if the order and the members of the two groups are the same, MPI_SIMILAR if only the members are the same, and MPI_UNEQUAL otherwise. ⭐
• _ierror_ — Fortran only, bestie: error status (integer). 😭

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🔥 DESCRIPTION

Okay so here's the tea, and it's so simple it's iconic:

MPI_IDENT results if the group members and the group order are exactly the same in both groups. This happens for instance if group1 and group2 are the same handle. Like, obviously. 💅

MPI_SIMILAR results if the group members are the same but the order is different. Same girlies, different lineup. 🦋

MPI_UNEQUAL results otherwise. That's it. No cap. 🙈

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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. Keep that in mind, fr fr.

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. Very main character, very dramatic. 💀
• 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. 🌸
• 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. Say it with me: no guarantees, 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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And that's the whole page, bestie — go compare some groups and slay. 💖✨🍓

Sep 11, 2026 · Open MPI · MPI_GROUP_COMPARE(3) — mwah, ily, bye! 💜🦋