Differential Equations › Section E · Systems of differential equations › Topic E.11

Nonlinear systems: equilibria and linearization

Most nonlinear systems have no solution formula, yet close to each equilibrium they behave almost exactly like a linear system. Finding the equilibria and linearising there gives a reliable local picture of the whole phase plane.

In this topic

  • Beyond linear systems
  • Equilibria and nullclines
  • The Jacobian and linearisation
  • Classifying with trace and determinant
  • When linearisation can be trusted
  • Worked example: competing species
  • Worked example: a damped pendulum
  • A centre that does not survive
  • Basins of attraction and separatrices
  • Common mistakes to avoid
  • Key takeaways

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