ompi.m File Reference

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Functions
function	ompi ()
	Return the MPI image count and the current image ID (e.g., MPI rank + 1) if the application has been launched via the OpenMPI mpiexec launcher. More...

Function Documentation

ompi()

function ompi

(

)

Return the MPI image count and the current image ID (e.g., MPI rank + 1) if the application has been launched via the OpenMPI mpiexec launcher.

This function attempts to detect the invocation of the current MATLAB session via an OpenMPI mpiexec binary MPI launcher instance.
The runtime detection is achieved by checking for runtime environment variables that the OpenMPI mpiexec binary executable defines upon launch.

Specifically, OpenMPI provides the following environment variables that are defined on every MPI process:

1. OMPI_COMM_WORLD_SIZE : The number of processes in this process MPI_COMM_WORLD.
   
2. OMPI_COMM_WORLD_RANK : The MPI rank of this process in MPI_COMM_WORLD.
   
3. OMPI_COMM_WORLD_LOCAL_SIZE : The number of ranks from this job that are running on this node.
   
4. OMPI_COMM_WORLD_LOCAL_RANK : The relative rank of this process on this node within its job.
   For example, if four processes in a job share a node, they will each be given a local rank ranging from 0 to 3.
5. OMPI_UNIVERSE_SIZE : The number of process slots allocated to this job.
   Note that this may be different than the number of processes in the job.
   
6. OMPI_COMM_WORLD_NODE_RANK : The relative rank of this process on this node looking across all jobs.
   

Returns

nproc : The output scalar MATLAB non-negative whole number containing the number of MPI images in the current invocation of the OpenMPI mpiexec binary MPI launcher.
An output value of 0 implies the algorithm failed to detect a ParaMonte-compatible OpenMPI library or failed to infer the image count.
rankp1 : The output scalar MATLAB non-negative whole number containing the image ID (e.g., MPI rank + 1) of the current MPI image in the current invocation of the OpenMPI mpiexec binary MPI launcher.
An output value of 0 implies the algorithm failed to detect a ParaMonte-compatible MPI library or failed to infer the image count.
Note that the image ID always starts at 1, unlike the MPI rank.
The argument rankp1 stands for rank + 1.
An output value of 0 implies the algorithm failed to detect a ParaMonte-compatible OpenMPI library or failed to infer the image count.

Possible calling interfaces ⛓

[nproc, rankp1] = pm.lib.mpi.runtime.ompi()

See also

pm.lib.mpi.runtime.mmpi()
pm.lib.mpi.runtime.impi()
pm.lib.mpi.runtime.ompi()
pm.lib.mpi.runtime.hydra()
pm.lib.mpi.runtime.nproc()
pm.lib.mpi.runtime.rankp1()
pm.lib.mpi.runtime.isimpi()
pm.lib.mpi.runtime.detect()

Example usage ⛓

cd(fileparts(mfilename('fullpath'))); % Change working directory to source code directory.
addpath('../../../../../'); % Add the ParaMonte library root directory to the search path.
 
disp('[nproc, rankp1] = pm.lib.mpi.runtime.ompi()')
      [nproc, rankp1] = pm.lib.mpi.runtime.ompi()
disp("")

Example output ⛓

[nproc, rankp1] = pm.lib.mpi.runtime.ompi()
nproc =
     0
rankp1 =
     0

Final Remarks ⛓

---

If you believe this algorithm or its documentation can be improved, we appreciate your contribution and help to edit this page's documentation and source file on GitHub.
For details on the naming abbreviations, see this page.
For details on the naming conventions, see this page.
This software is distributed under the MIT license with additional terms outlined below.

1. If you use any parts or concepts from this library to any extent, please acknowledge the usage by citing the relevant publications of the ParaMonte library.
   
2. If you regenerate any parts/ideas from this library in a programming environment other than those currently supported by this ParaMonte library (i.e., other than C, C++, Fortran, MATLAB, Python, R), please also ask the end users to cite this original ParaMonte library.
   

This software is available to the public under a highly permissive license.
Help us justify its continued development and maintenance by acknowledging its benefit to society, distributing it, and contributing to it.

Copyright

Computational Data Science Lab

Author:

Fatemeh Bagheri, May 20 2024, 1:25 PM, NASA Goddard Space Flight Center (GSFC), Washington, D.C.
Amir Shahmoradi, 12:10 AM Wednesday, November 13, 2024, NASA Goddard Space Flight Center (GSFC), Washington, D.C.