Linear Systems and Eigenmodes — Cheat sheet

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Core rule

Av=λv  ⟹  x(t)=eλtv.A\mathbf v=\lambda\mathbf v\implies\mathbf x(t)=e^{\lambda t}\mathbf v.

Watch for

Eigenvectors describe state directions, which may mix quantities with different physical units. Define the state and scaling before interpreting a phase-plane angle as a physical angle.