Attractors

Level AdvancedDifficulty ★★★★★Concept⌖ Open in the map

What is it?

Sets that nearby trajectories approach and stay in: a point, a closed orbit (limit cycle) or a fractal "strange attractor" like Lorenz's butterfly. The set of initial states that end up there is its basin.

Formulas

x˙=σ(y−x),y˙=x(ρ−z)−y,z˙=xy−βz\dot x = \sigma(y - x), \quad \dot y = x(\rho - z) - y, \quad \dot z = xy - \beta z
Lorenz system (σ=10\sigma = 10, ρ=28\rho = 28, β=8/3\beta = 8/3)

Where it shows up in computing

  • Weather and climate modelling★★★★★frequentPhysics and simulation

    Lorenz found his attractor in a toy convection model; climate can be seen as the statistics of the attractor, weather as a point on it.

Where it shows up in AI

  • Neural networks★★★★★historicalAI and machine learning

    Hopfield networks store memories as point attractors of an energy-descending dynamics (Nobel Prize in Physics 2024).

Where is it used?

Computing topics reachable from here, through the chain of ideas that leads to them:

What depends on it

This page has the essentials. A fuller treatment (intuition, formal definition, worked example) is on the way.

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