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fuzzy logic

a branch of logic designed to allow degrees of imprecision in reasoning and knowledge, typified by terms such as `very', `quite possibly', and `unlikely', to be represented in such a way that the information can be processed by computer
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
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fuzzy logic in Science
fuzzy logic
A form of algebra employing a range of values from "true" to "false" that is used in making decisions with imprecise data. The outcome of an operation is assigned a value between 0 and 1 corresponding to its degree of truth. Fuzzy logic is used, for example, in artificial intelligence systems.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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fuzzy logic in Technology

A superset of Boolean logic dealing with the concept of partial truth -- truth values between "completely true" and "completely false". It was introduced by Dr. Lotfi Zadeh of UCB in the 1960's as a means to model the uncertainty of natural language.
Any specific theory may be generalised from a discrete (or "crisp") form to a continuous (fuzzy) form, e.g. "fuzzy calculus", "fuzzy differential equations" etc. Fuzzy logic replaces Boolean truth values with degrees of truth which are very similar to probabilities except that they need not sum to one. Instead of an assertion pred(X), meaning that X definitely has the property associated with predicate "pred", we have a truth function truth(pred(X)) which gives the degree of truth that X has that property. We can combine such values using the standard definitions of fuzzy logic:
truth(not x) = 1.0 - truth(x) truth(x and y) = minimum (truth(x), truth(y)) truth(x or y) = maximum (truth(x), truth(y))
(There are other possible definitions for "and" and "or", e.g. using sum and product). If truth values are restricted to 0 and 1 then these functions behave just like their Boolean counterparts. This is known as the "extension principle".
Just as a Boolean predicate asserts that its argument definitely belongs to some subset of all objects, a fuzzy predicate gives the degree of truth with which its argument belongs to a fuzzy subset.
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James Brule, "Fuzzy systems - a tutorial", 1985 (
STB Software Catalog (, includes a few fuzzy tools.
[H.J. Zimmerman, "Fuzzy Sets, Decision Making and Expert Systems", Kluwer, Dordrecht, 1987].
["Fuzzy Logic, State of the Art", Ed. R. Lowen, Marc Roubens, Theory and Decision Library, D: System theory, Knowledge Engineering and Problem Solving 12, Kluwer, Dordrecht, 1993, ISBN 0-7923-2324-6].
The Free On-line Dictionary of Computing, © Denis Howe 2010
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