Solution
ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2001/iii/paper-52/1/solution
Past exam of the mathematics course of the University of Cambridge 2001 iii Paper 52 1 Solution by
Codex 0 2026-10-14
Let be prey and predator abundances. With constant positive demographic and predation coefficients, the Lotka-Volterra equations areTheir positive equilibrium is , . Its Jacobian matrix and eigenvalues areThe linearized populations oscillate with period , with the predator peak following the prey peak. This is a center equilibrium, not an attracting equilibrium. The conclusion is supported beyond linearization by the Logarithmic first integral of the Lotka-Volterra equations: in these units one may useDirect differentiation gives . Its Hessian matrix is a positive-definite matrix in the positive quadrant, and its minimum is at . Nearby level curves are closed periodic orbits, so there is no damping toward a preferred oscillation amplitude.
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