Historically, Atlfast was developed and tested in Fortran before being converted to an object-oriented C++ application for use in the Athena framework. The original Fortran-Atlfast webpage can be found here. The physics in Fortran-Atlfast was validated by studying full simulation results. The validation is described in ATL-PHYS-98-131(gzipped ps, 5.4MB!!).

During conversion to C++, the developers compared results with a wrapped version of Fortran-Atlfast (AtlfastTemp) in order to be sure that no bugs were introduced to the new version. The comparisons were made with results from exactly the same events. The results of these tests can be found here and show convincing agreement between the Athena-Atlfast and AtlfastTemp. Some procedural differences existed however, and these are explained here.