Computer Explorations of Fractals, Chaos,Complex Systems, and Adaptation

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 Glossary - U

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# U

Uncountable Infinity     An order of infinity that is larger than the number of natural numbers. The number of real numbers is uncountably infinite.

Universal Approximation     Having the ability to approximate any function to an arbitrary degree of accuracy. Neural networks are universal approximators.

Universal Computation     Capable of computing anything that can in principle be computed; being equivalent in computing power to a Turing machine, the lambda calculus, or a Post production system.

Universal Computer     A computer that is capable of universal computation, which means that given a description of any other computer or program and some data, it can perfectly emulate this second computer or program. Strictly speaking, home PCs are not universal computers because they have only a finite amount of memory. However, in practice, this is usually ignored.

Unstable     Having a basin of attraction that is 0 in size; being such that the slightest perturbation will forever change the state of a system. A pencil balanced on its point is unstable.

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