backtracking

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backtracking

[′bak‚trak·iŋ]
(computer science)
A method of solving problems automatically by a systematic search of the possible solutions; the invalid solutions are eliminated and are not retried.

backtracking

(algorithm)
A scheme for solving a series of sub-problems each of which may have multiple possible solutions and where the solution chosen for one sub-problem may affect the possible solutions of later sub-problems.

To solve the overall problem, we find a solution to the first sub-problem and then attempt to recursively solve the other sub-problems based on this first solution. If we cannot, or we want all possible solutions, we backtrack and try the next possible solution to the first sub-problem and so on. Backtracking terminates when there are no more solutions to the first sub-problem.

This is the algorithm used by logic programming languages such as Prolog to find all possible ways of proving a goal. An optimisation known as "intelligent backtracking" keeps track of the dependencies between sub-problems and only re-solves those which depend on an earlier solution which has changed.

Backtracking is one algorithm which can be used to implement nondeterminism. It is effectively a depth-first search of a problem space.
References in periodicals archive ?
The efficiency comes primarily from the high-yield backtracking search strategy.
A human-level AI must either integrate, for example, backtracking search, partially observable Markov decision processes (POMDPs), logic theorem proving algorithms, productions systems, and neural networks, or it must be based on new, heretofore undiscovered computational methods that exhibit all of the best features of these computational methods.
Fahiem Bacchus (University of Toronto), the third invited speaker, presented his work on the use of caching in backtracking search.