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iSGTW Feature - Gridifying Geant4

Feature - Gridifying Geant4

Simulation of the nuclear reaction of a cosmic-ray proton in one of the inertial sensors of the Laser Interferometer Space Antenna. LISA is a joint ESA-NASA mission for the first space-borne gravitational wave detector.
Image courtesy of Geant4

Twice a year a new version of the Geant4 software is released to the research community. Geant4, a software toolkit that simulates the interactions of particles with scientific instruments, is used by high-energy physicists, space scientists, medical physicists and radiation researchers. These simulations can help engineers alter instrument design for optimal performance or teach researchers how to best analyze their data.

Before a release, the new version of Geant4 must be carefully tested. Evaluators from the Geant4 development team compare the simulation results of two previous Geant4 versions, looking for significant differences. Since December 2004, these tests have been run at several Worldwide LHC Computing Grid sites using the EGEE infrastructure. Grid computing accelerates the evaluation process dramatically: the whole test suite contains about 15,000 jobs; on a single computer the evaluation would take four years.

When a discrepancy is found, a Geant4 expert examines the test statistics to understand the cause. Differences usually arise from improved features in the new version, or problems in the old version that have been fixed in the new.

The test suite is based on the simulation of a set of sampling calorimeters, devices to sense heat output, which are hit by a class of particles at varying energies. The tests are designed to suit the needs of the physicists and detectors at CERN's Large Hadron Collider.

During the first week of testing, the Geant4 team distributes software to selected sites participating in the WLCG. By the second week, testing is at full production-running Geant4 jobs, or work requests, on the grid.

The Geant4 collaboration has been a virtual organization within EGEE since December 2005. Several WLCG sites provide computing resources to the Geant4 VO to increase their testing performance. Last summer, the Geant4 team was able to further optimize production by incorporating the Ganga/DIANE framework. This framework, distributed by the ARDA team at CERN, controls job distribution and makes the run time easier to predict. Testers now can better plan the stages of production and need not be as manually involved in the process.

For further information on Geant4 production see this recent article in the CERN Computer Newsletter.

- Patricia Mendez Lorenzo
Geant4 Production team, CERN

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