In a reachability probability problem, one wants to compute the
probability *p* to reach a final state *s+*, from the initial state
*s0* of a given model. When the size of the model becomes too
large for numerical analysis and when the probability of
interest *p* is too small for direct statistical simulation,
rare event acceleration methods become necessary. A possible approach
to tackle this problem is to build an importance sampling scheme for
which a statistical simulation becomes possible. In order to be
useful, this importance sampling has to be built carefully to ensure a
reduction of the variance. In
[16,17]
a method to to produce suche an importrance sampling is described. This approache have been implemented in Cosmos and
have been succesfully applied to waiting queue example as well as a biological case study [9,12].