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Artificial Intelligence and Soft Computing: Behavioral ... - Arteimi.info

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(concept) space by generalization <strong>and</strong> specialization rules. Lex generalizes<br />

expressions by replacing a symbol by its ancestors following a generalization<br />

tree grammar. A portion of the generalization tree grammar is given in fig.<br />

13.2.<br />

trig<br />

Function(arguments)<br />

primary Comb (f1,f2)<br />

trans Polynomial<br />

sin cos tan<br />

ln log<br />

Fig. 13.2: A segment of the LEX generalization tree.<br />

The architecture of LEX comprises four basic modules, as shown in<br />

fig.13.3. For the sake of training, the problem generator generates sample<br />

training problems <strong>and</strong> the problem solver attempts to solve it by employing<br />

available heuristics <strong>and</strong> operators. A solution is obtained when the operator<br />

yields an expression free from integration. The critic analyses the solution<br />

trace <strong>and</strong> produces positive <strong>and</strong> negative training instances from the solution<br />

trace. The generalizer performs c<strong>and</strong>idate elimination to learn new heuristics.<br />

learned<br />

heuristics<br />

Problem<br />

Generator<br />

Generalizer<br />

training<br />

instances<br />

labeled<br />

training<br />

operators<br />

Problem<br />

Solver<br />

Critic<br />

Fig. 13.3: The architecture of LEX.<br />

solution<br />

traces

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