Am 04.01.2014 13:44, schrieb Richard Clark: > Take the function f(x,y) = (sin(y)+x, sin(sin(y)+x)+y) > > This has fixed points at (n.pi,m.pi) for integer values of n and m. > > These are alternately centres and saddle points. > > If you start an iteration of the function close to one of the centres e.g. (pi,0) you go around a loop containing the centre forever. > > If, however, you start the iteration of the function close to one of the saddle > points, e.g. (0,0), an interesting thing happens: it goes around one of the adjacent centres a certain number of times, then goes starts going around a centre adjacent to the original centre a certain number of times, then starts going around a centre adjacent to THAT centre a certain number of times etc. > > How many times it goes around the centre, and which of the 4 adjacent centres it then starts going around is sensitive to initial conditions.
Actually, your map f lifts to a map on the torus if you look at x and y modulo 2*Pi. The map then only has two centres at (0,Pi) and (Pi,0) and two saddles at (0,0) and (Pi,Pi). Still fun to play around with.