The exit a particle eventually takes is sensitively dependent on
its initial condition which is specified by its original location
(x0 and the distance b above the x-axis) and its initial
direction of approach (angle 
with respect to the y-axis). The scattering region is
defined as the shaded region in the diagram. We are interested
in trajectories that enters the scattering region at some point
and eventually leaves through one of the exits.
In all subsequent computation,
the following values are used: R = 1.8, L = 4.0, x0 = -4.0, and
the vertices of the triangle are (0,0), (0.69,3.94), (3.76,1.37).
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