,
where 
are action variables, 
are
their conjugated
The web of Resonances: the background represents the web of resonances of the quasi-integrable Hamiltonian:
,
where
are action variables, are
their conjugated
angles, and 
is small. The set of lines in the picture represents the projection
of the resonances of
the system on the plane of the actions 
,
while the uniform background color represent the set of invariant
tori. The numerical method to obtain such a kind of pictures is described in the paper by Froeschle' C., Guzzo M. and
Lega E. :``Graphical
Evolution of the Arnold Web: From Order to Chaos'' published in
Science, Volume 289, n. 5487, 2000.