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

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 Glossary - H

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# H

Halting Problem     The problem of determining if a program halts or doesn't halt on a particular input. This is an incomputable problem.

Halting Set     The recursively enumerable set of Gödel numbers that correspond to programs that halt if given their own Gödel number as input.

Hebbian Learning     A rule that specifies that the strength of a synapse between two neurons should be proportional to the product of the activations of the two neurons. cd

Hénon Map     A chaotic system (defined by the two equations x(t+1) = a - x(t)^2 + b y(t) and y(t+1) = x(t)) that has a fractal strange attractor and operates in discrete time.

Hidden Layer     In a feedforward or recurrent neural network, a layer of neurons that is neither the input layer nor the output layer but is physically between the two.

Hill-Climbing     One of the simplest search methods that attempts to find a local maximum by moving in an uphill direction. It is related to steepest ascent. Hill-climbing may use gradient information, or random sampling of nearby points, in order to estimate the uphill direction.

Holism     The idea that ``the whole is greater than the sum of the parts.'' Holism is credible on the basis of emergence alone, since reductionism and bottom-up descriptions of nature often fail to predict complex higher-level patterns. See also top-down.

Hopfield Network     A type of feedback neural network that is often used as an associative memory or as a solution to a combinatorial optimization problem.

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