Past exam of the mathematics course of the University of Cambridge 2003 iii Paper 59 3 b Solution Created 2026-10-03 Updated 2026-10-14
We count periodic orbits whose trajectories remain near the two specified homoclinic orbits; the local hypotheses impose no bound on unrelated distant cycles. Choose the return domain small enough that and are less than one. Each admissible return branch is then a contraction mapping.
A right-lobe periodic orbit is a fixed point with and . For small amplitudes it exists exactly when , and . Similarly, a left-lobe periodic orbit has , , , and exists for . Their Floquet multipliers tend to zero, so both are attracting.
A period-two orbit of the section map corresponds to one flow periodic orbit traversing both lobes. Write its states as and . Its positive amplitudes satisfyThe two-step derivative is , again tending to zero. The asymmetric planar gluing return map therefore gives at most one such attracting two-lobe cycle in the small domain. Its boundaries are obtained by setting one amplitude to zero:For the original flow these are leading equations, with corrections or . On , the negative unstable branch makes both excursions before returning to the positive stable branch; on the positive unstable branch returns to the negative stable branch. Each is a compound homoclinic orbit, with one extra passage near the saddle equilibrium. They are distinct from the primary loop curves and .
The six open regions and their local cycles are:
| Region | Attracting flow cycles |
|---|---|
| Right and left single-lobe cycles | |
| Right single-lobe cycle only | |
| Right single-lobe cycle and two-lobe cycle | |
| Left single-lobe cycle only | |
| Left single-lobe cycle and two-lobe cycle | |
| Two-lobe cycle only |
There is no additional small alternating cycle when both parameters are negative. Indeed the two positive-amplitude equations would imply and , giving , impossible for sufficiently small positive . On each mixed-sign quadrant the contraction equations give the two-lobe cycle precisely on the side of the compound curve toward the positive quadrant.
On , there is the primary right homoclinic orbit, together with a left cycle if or a two-lobe cycle if . On the analogous statement holds with left and right interchanged. On there is a compound homoclinic orbit and the right single-lobe cycle; on there is a compound homoclinic orbit and the left single-lobe cycle. At the two primary loops meet at the same saddle equilibrium. The approach to each homoclinic orbit has a diverging period; it is not a saddle-node collision of two finite-period cycles.
Parameter regions and schematic phase portraits for asymmetric planar gluing
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