Running

This page gives information on how to run nekRS has been installed (see Installing ) and appropriate input files have been generated (see Case files).

nekrs and nekrs32

Native Running

The most basic way of running nekRS is in the directory with all the appropriate files with the scenario name:

mpirun -np <number of MPI tasks> nekrs --setup <scenario>.par

Below are the command line arguments that can be used to further modifiy how nekRS is run.

Parameter	Short option	Options	Description	Required
--help	-h	None or par	Print help, either summary of command line argument	No
--setup	-s	None, par or sess file	Specifies the location of files needed to initialise the simulation	Yes
--build-only	-b	None or #procs	Initialise the simulation and run Just-in-time Compilation only.	No
--cimode	-c	None or <id> (N.B. If set must be >=0)	Runs specific CI tests if available in the chosen simulation (see Contributing)	No
--debug	-d	None	Run in debug mode, IE print values of many of the variables while running	No
--backend	-t	CPU, CUDA, HIP, DPCPP or OPENCL	Manually set the backend device for running	No
--device-id	-i	id or LOCAL-RANK	Manually set OCCA device ID (I.E. for machines with multiple GPUs) or use LOCAL-RANK for CPU	No

MPI launch scripts

A number of scripts ship with nekRS itself and are located in the $NEKRS_HOME/bin directory (see Set NEKRS_HOME). A brief summary of these scripts and their usage is as follows.

• nrsmpi <casename> <processes>: run nekRS in parallel with <processes> parallel processes for the case files that are prefixed with casename.

• nrsbmpi <casename> <processes>: same as nrsmpi, except that nekRS runs in the background

Queueing system

TODO