# 4.4. Batch running (cbcbatch)¶

When you’ve set up a simulation in a python file, you can investigate a range of parameters through the shell script cbcbatch. This allows you to easily run simulations required to for example compute convergence rates or parameter sensitivity with respect to some compute Field.

Based on the parameters of your solver or problem, you can set up parameter ranges with command line arguments to cbcbatch. Say for example that you wish to investigate the effects of refinement level N and timestep dt over a given range. Then you can launch cbcbatch by invoking

cbcbatch run.py N=[8,16,32,64,128] dt=[0.1,0.05,0.025,0.0125] \
casedir=BatchResults


where run.py is the python file to launch the simulation. This will then add all combinations of N and dt (5*4=20) to a queue, and launch simulations when the resources are available. We call dt and N the batch parameters.

By default, cbcbatch runs on a single core, but this can be modified by setting the num_cores argument:

cbcbatch run.py N=[8,16,32,64,128] dt=[0.1,0.05,0.025,0.0125] \
casedir=BatchResults num_cores=8


This will cause 8 simulations to be run at a time, and new ones started as soon as one core becomes available. Since there may be a large variations in computational cost between parameters, it is also supported to tie one of the batch parameters to run in parallel with mpirun:

cbcbatch run.py N=[8,16,32,64,128] dt=[0.1,0.05,0.025,0.0125] \
casedir=BatchResults num_cores=8 mpirun=[1,1,2,4,8] \
mpirun_parameter=N


This command will run all simulations with N=1 and N=2 on a single core, N=32 on 2 cores, N=64 on 4 cores and N=128 on 8 cores.

Important

The runnable python file must set set_parse_command_line_arguments(True) to be run in batch mode.

Important

The command line parameters casedir, mpirun, mpirun_parameter and num_cores are reserved for cbcbatch and can thus not be used as batch parameters.