Internal-wave ray return map
= Internal-wave ray return map
{title2=$x_{n+1}=R(x_n)$}
Map one boundary intersection of an <internal-wave ray> to the next intersection with the same boundary after a specified reflection itinerary. A periodic ray is a fixed point. Linear contraction, $|R'|<1$, gives an <internal-wave attractor>; the reversed itinerary, when invertible, has reciprocal multiplier and is locally repelling.