MPI_GROUP_RANGE_EXCL(3)

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💅 MPI_GROUP_RANGE_EXCL(3) — Open MPI, bestie edition ✨

okay so this is the MPI_GROUP_RANGE_EXCL page from the Open MPI manual, and it's genuinely so useful — it's literally how you build a brand new group by excluding whole ranges of processes from a group you already have. no cap, it's giving constructor energy but for groups 🫶

🌸 NAME 🌸

MPI_Group_range_excl — produces a group by excluding ranges of processes from an existing group.

like, you hand it a group and a bunch of rank ranges and it hands you back a group with those ranks yeeted out. iconic behaviour honestly 💅

✨ SYNTAX ✨

🎀 C Syntax 🎀

#include <mpi.h>

int MPI_Group_range_excl(MPI_Group group, int n, int ranges[][3],
     MPI_Group *newgroup)

🎀 Fortran Syntax 🎀

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_GROUP_RANGE_EXCL(GROUP, N, RANGES, NEWGROUP, IERROR)
     INTEGER GROUP, N, RANGES(3,*), NEWGROUP, IERROR

🎀 Fortran 2008 Syntax 🎀

USE mpi_f08
MPI_Group_range_excl(group, n, ranges, newgroup, ierror)
     TYPE(MPI_Group), INTENT(IN) :: group
     INTEGER, INTENT(IN) :: n, ranges(3,n)
     TYPE(MPI_Group), INTENT(OUT) :: newgroup
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

🌈 INPUT PARAMETERS 🌈

  • group — Group (handle). this is the group you're starting from, your main character group if you will 👑
  • n — Number of triplets in array ranges (integer). like, how many little ranges you're throwing at it 🍓
  • ranges — A one-dimensional array of integer triplets of the form (first rank, last rank, stride), indicating the ranks in group of processes to be excluded from the output group newgroup. so each triplet is like "from here to here, stepping like this" and everything it touches gets dropped 💀

💖 OUTPUT PARAMETERS 💖

  • newgroup — New group derived from above, preserving the order in group (handle). yes bestie, the order is preserved, that's the whole vibe ⭐
  • ierror — Fortran only: Error status (integer). the Fortran girlies get their error code in the last argument, as always 🙈

🦋 DESCRIPTION 🦋

okay so here's the actual tea: each computed rank must be a valid rank in group, and all computed ranks must be distinct, or else the program is erroneous. like, that's not a suggestion, that's the rule — break it and it's erroneous, periodt 🚨

the functionality of this routine is specified to be equivalent to expanding the array of ranges to an array of the excluded ranks and passing the resulting array of ranks and other arguments to MPI_Group_excl. so like, same energy, different packaging 🎁

and a call to MPI_Group_excl is equivalent to a call to MPI_Group_range_excl with each rank i in ranks replaced by the triplet (i,i,1) in the argument ranges. see? one rank is just a tiny little range with stride 1, iykyk 🧚

🔥 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.

so yeah, the handler situation has layers, but that's the whole rundown, no detail skipped 💅

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, it just hands you the code and lets you deal 🫶

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, bestie, don't assume you can just keep going after an error, that's genuinely not promised 😭

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_Group_excl
  • MPI_Group_free

2003-2026, The Open MPI Community

and that's the whole page, bestie! 🎀 this was the Open MPI MPI_GROUP_RANGE_EXCL(3) man page, dated Sep 11, 2026 — go forth and exclude those ranges responsibly, mwah 💋🌸

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