  The chaotic or ordered character of orbits in galactic models is an important
issue, since it can influence dynamical evolution. This distinction can be
achieved with the help of the Smaller Alingment Index - (SALI). We describe
here briefly this method and its advantages. Then we apply it to that case of
2D and 3D barred galaxy potentials. In particular, we find the fraction of
chaotic and ordered orbits in such potentials and present how this fraction
changes when the main parameters of the model are varied. For this, we consider
models with different bar mass, bar thickness or pattern speed. Varying only
one parameter at a time, we find that bars that are more massive, or thinner,
or faster, have a larger fraction of chaotic orbits.

Astrophysics