Table of Contents

• Usage
• Structure of the output file

Usage

Typing restG4 -h will show all available options.

Basic Usage

restG4 simulation.rml will launch a simulation using simulation.rml as the configuration file. The output file will be saved to the specified path in the configuration.

Multithreading

restG4 makes use of the multithreading capabilities of Geant4 and can be used in multithreading mode to significantly increase simulation speed.

• restG4 simulation.rml -t 8 will launch a simulation using 8 worker threads.

By default restG4 is executed in serial mode (one single thread) and is equivalent to the -t 0 option.

Simulation results are determined by the random seed and the number of threads, so using different number of threads with the same seed will produce different results. Using the same seed and same number of threads produces the same results.

The multithreading implementation of restG4 is new and although it looks to be working properly it may have some bugs. If you find one of such bugs, please post an issue here with the multithreading label.

We encourage our users to use the multithreading feature especially when performing exploratory simulations.

Overriding values from the RML

The CLI interface allows to set a few different parameters without having to modify the RML.

• restG4 simulation.rml -o output.root to specify the output file.
• restG4 simulation.rml -n 1000 to set the number of processed events (n in Geant4's /run/beamOn n or nEvents in the rml configuration).
• restG4 simulation.rml -g geometry.gdml to specify the geometry file.

Ending the simulation early

The simulation run will naturally end when the selected number of events have been processed. They can either be specified in the RML file or via the -n flag on the CLI. However, the user can also specify additional conditions to end the simulation early.

• restG4 simulation.rml -e 1000 will signal the simulation to stop once 1000 events have been marked as valid (saved on the output file). The final simulation will probably have a slightly higher number of entries than the value specified in the case of multithreading as the worker threads may still be working on valid events, or they may not have been saved yet. The number of processed events (the equivalent of nEvents) will be adjusted to the real number of processed events, overriding the selected value of the user, so the resulting simulation would be equivalent to a plain simulation using this value as nEvents. This holds more accurately the large the -N parameter.
• restG4 simulation.rml --time 1h20m30s will signal the simulation to stop after 1 hour 20 minutes and 30 seconds have elapsed since the start. You can specify any value using this format such as 1h15m, 30s, etc.
• Sending the interrupt signal (typically via CTRL+C) will signal the simulation to stop, and it will attempt to save the results into disk before closing the process.

Structure of the output file

TODO