Concept
Lyapunov exponent
The average rate at which two nearby orbits of a map separate, measured as the logarithm of a factor per step. A positive value is what chaos means quantitatively, and its reciprocal is how many steps a computed orbit tracks the true one before the rounding has been amplified to full size.
Named by 2 essays across one field — each of them below, with the objects they name alongside it.
How fast two orbits part
The word "sensitive" is an adjective. Averaging the logarithm of one derivative along an orbit turns it into a number — one that says how many steps of prediction the map allows, and whose sign says whether it allows any.
The same map in different coordinates
The tent map and the logistic map at four look nothing alike and are the same map, carried onto each other by a change of variable. Everything either one does the other does, and the change of variable is a sine squared.
Named alongside it
The objects these essays reach for when they reach for this one.
Logistic mapAverageBifurcationChange of variableChaosConjugacyDerivativeHomeomorphismIterationLogarithmOrbitPeriodic orbit