hydra.m File Reference

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

Function Documentation

hydra()

function hydra

(

)

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

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

Specifically, a Hydra-basedMPI provides an informal list of environment variables that are defined on every MPI process.
These variables may not be defined on all platforms.
Some are only defined at runtime, while others are defined at compile-time.

1. On Unix systems, the best approach to investigate the Hydra-MPI-specific runtime variables is to launch a Hydra-based mpiexec binary executable with the printenv Unix command.
   

   mpiexec -np 1 printenv

   To see the compile-time variables and compare them with the runtime list from the above, try:
   

   printenv

2. On Windows systems, the best approach to investigate the Hydra-specific runtime variables is to launch a Hydra-based mpiexec binary executable with the set Windows batch command.
   

   mpiexec -n 1 cmd /k set

   To see the compile-time variables and compare them with the runtime list from the above, try:
   

   set

   Note that as of 2024, the only ParaMonte-compatible Hydra-based MPI library on Windows is the Intel MPI library.
   

The most persistent environment variables for Hydra-based mpiexec binary appear to be the following:

1. PMI_RANK : The rank of the current process in the current MPI communication world.
   
2. PMI_SIZE : The size (i.e., number of images/processes) of the current MPI communication world.
   
3. MPI_LOCALRANKID : The local rank of the current process relative to the local host.
   This environment variable may not be defined on all platforms (e.g., Windows) by all Hydra-based MPI libraries.
   
4. MPI_LOCALNRANKS : The size (i.e., number of images/processes) of the current MPI communication on the local host.
   This environment variable may not be defined on all platforms (e.g., Windows) by all Hydra-based MPI libraries.
   

Returns

nproc : The output scalar MATLAB non-negative whole number containing the number of MPI images in the current invocation of a Hydra-based MPI mpiexec binary MPI launcher.
An output value of 0 implies the algorithm failed to detect a ParaMonte-compatible Hydra-based MPI 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 a Hydra-based 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 Hydra-based MPI library or failed to infer the image count.

Possible calling interfaces ⛓

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

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.hydra()')
      [nproc, rankp1] = pm.lib.mpi.runtime.hydra()
disp("")

Example output ⛓

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