Elementary equilibrium bifurcation models
A bifurcation is a qualitative change in a parameterized dynamical system.
Key knowledge
A bifurcation is a qualitative change in a parameterized dynamical system. In dimensionless normal forms, x′=μ−x² creates stable +√μ and unstable −√μ equilibria for μ>0; x′=μx−x² exchanges stability between x=0 and x=μ; x′=μx−x³ changes x=0 from stable to unstable as two stable branches ±√μ appear for μ>0.
Values and equations
dx/dτ=μ−x²; dx/dτ=μx−x²; dx/dτ=μx−x³
- x
- Dimensionless rescaled state
- τ
- Dimensionless rescaled time
- μ
- Dimensionless bifurcation control parameter
Conditions and scope
- Local smooth one-dimensional models near the relevant critical parameter, rescaled time/state; the three forms are saddle-node, transcritical and supercritical pitchfork respectively.
- Pitchfork and transcritical persistence requires symmetry/structural constraints; generic perturbations can unfold them. At μ=0 the strict linear test is inconclusive and each nonlinear form determines the critical behavior.
Sources · 1
References
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Evidence and review
Classical Mechanics III 8.09 (2014): Chapter 7, nonlinear dynamics: §7.2.1–7.2.3 printed pages 153–159: saddle-node diagrams for r±x², transcritical exchange and supercritical pitchfork equation 7.32. Derivative signs determine the stated branches; r relabeled μ.
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