Solution

ID: past-exam-of-the-differential-equations-and-applications-course-of-the-university-of-oxford/2009/a/1/c/solution

On the attracting right branch, and , so the motion goes from towards the fold . At essentially fixed it jumps to the other attracting root . The left branch then carries it to , where it jumps right to . This gives the clockwise limiting relaxation oscillation shown in the preceding figure.
Along a slow branch , differentiation gives . The right-branch time is
Reflection symmetry gives the same time on the left. The fast jumps take a time tending to zero as , as do the fold-transition corrections at leading order. Hence
This is a leading asymptotic period, not an exact finite- equality.

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