sci-physics@gentoo.org Gentoo Physics Project The Virtual Monte Carlo (VMC) allows to run different simulation Monte Carlo without changing the user code and therefore the input and output format as well as the geometry and detector response definition. The core of the VMC is the category of classes vmc in ROOT. It provides a set of interfaces which completely decouple the dependencies between the user code and the concrete Monte Carlo. Geant3 VMC (C++) is provided within a single package together with GEANT3 (Fortran) - geant3. Enable the Virtual Geometry Model (sci-physics/vgm) Build G4Root (interface for GEANT4 simulation with a ROOT geometry) Build with Geant4 G3toG4 library Build MTRoot (provides ROOT IO manager classes with multi-threading support)