  Triple-GEM detectors are a well known technology in high energy physics. In
order to have a complete understanding of their behavior, in parallel with on
beam testing, a Monte Carlo code has to be developed to simulate their response
to the passage of particles. The software must take into account all the
physical processes involved from the primary ionization up to the signal
formation, e.g. the avalanche multiplication and the effect of the diffusion on
the electrons. In the case of gas detectors, existing software such as Garfield
already perform a very detailed simulation but are CPU time consuming. A
description of a reliable but faster simulation is presented here: it uses a
parametric description of the variables of interest obtained by suitable
preliminary Garfield simulations and tuned to the test beam data. It can
reproduce the real values of the charge measured by the strip, needed to
reconstruct the position with the Charge Centroid method. In addition,
particular attention was put to the simulation of the timing information, which
permits to apply also the micro-Time Projection Chamber position
reconstruction, for the first time on a triple-GEM. A comparison between
simulation and experimental values of some sentinel variables in different
conditions of magnetic field, high voltage settings and incident angle will be
shown.
