MPI_DIST_GRAPH_NEIGHBORS_COUNT(3)

🌸 MPI_Dist_graph_neighbors_count 🌸

okay so bestie, welcome to the Open MPI manual page for MPI_Dist_graph_neighbors_count. 💖

This lil icon returns the number of in and out edges for the calling processes in a distributed graph topology, plus a flag telling you whether that distributed graph is weighted. that's it. that's the whole vibe. 🦋

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✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

int MPI_Dist_graph_neighbors_count(MPI_Comm comm, int *indegree,
     int *outdegree, int *weighted)

🎀 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_DIST_GRAPH_NEIGHBORS_COUNT(COMM, INDEGREE, OUTDEGREE, WEIGHTED, IERROR)
     INTEGER COMM, INDEGREE, OUTDEGREE, IERROR
        LOGICAL WEIGHTED

🎀 Fortran 2008 Syntax

USE mpi_f08
MPI_Dist_graph_neighbors_count(comm, indegree, outdegree, weighted, ierror)
     TYPE(MPI_Comm), INTENT(IN) :: comm
     INTEGER, INTENT(IN) :: indegree, outdegree
     INTEGER, INTENT(OUT) :: weighted
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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📥 INPUT PARAMETERS 📥

• comm — the communicator that's carrying the distributed graph topology, as a handle. this is your main character input, everything else is just receipts. 💅

📤 OUTPUT PARAMETERS 📤

• indegree — the number of edges into this process. it's a non-negative integer, so no negativity allowed bestie. 🙈
• outdegree — the number of edges out of this process. also a non-negative integer. so many edges, so little time. ✨
• weighted — false if MPI_UNWEIGHTED was supplied during creation, true otherwise. (it's a logical, so like, a truth-y situation.) ⚖️
• ierror — Fortran only: error status (integer). 🫶

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💖 DESCRIPTION 💖

MPI_Dist_graph_neighbors_count and MPI_Graph_neighbors provide adjacency information for a distributed graph topology. 📊

MPI_Dist_graph_neighbors_count returns the number of sources and destinations for the calling process. literally just "how many people are sliding into my inbox, and how many am I sliding into". iconic. 👑

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💀 ERRORS 💀

Almost all MPI routines return an error value: C routines hand it back as the return result of the function, and Fortran routines drop it 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. so many handlers, so much drama 🌈

Open MPI includes three predefined error handlers that can be used:

• MPI_ERRORS_ARE_FATAL — Causes the program to abort all connected MPI processes. it's giving nuclear. 💀
• 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. so like, handle your business, 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.

See also:

• MPI_Dist_graph_neighbors

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👑 Copyright 👑

2003-2026, The Open MPI Community

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okay that's the page!! 🎀 this was Open MPI's MPI_DIST_GRAPH_NEIGHBORS_COUNT(3) manual page, and the date on this baddie is Sep 10, 2026. now go count your edges, bestie — in and out. 💅✨🦋