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

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6. Pn- Γ the set of paths from node n to the set of goals Γ<br />

7. g* (n) the cheapest cost of paths, going from starting (root)<br />

node s to node n,<br />

g* (n) = K (s, n)<br />

8. h* (n) the cheapest cost of paths, going from node n to Γ,<br />

h* (n) = Min K (n, γ) , for all γ ε Γ<br />

9. C* the cheapest cost of paths going from s to Γ,<br />

C* = h* (s)<br />

We now define the following properties of best first search algorithms.<br />

a) Completeness: An algorithm is said to be complete, if it<br />

terminates with a solution, when one exists.<br />

b) Admissibility: An algorithm is called admissible if it is<br />

guaranteed to return an optimal solution, whenever a solution exists.<br />

c) Dominance: An algorithm A1 is said to dominate A2, if every<br />

node exp<strong>and</strong>ed by A1 is also exp<strong>and</strong>ed by A2.<br />

d) Optimality: An algorithm is said to be optimal over a class of<br />

algorithms, if it dominates all members of the class.<br />

We now present here some of the interesting properties of the heuristic<br />

functions.<br />

Property I: Any node n* on an optimal path P* γ - Γ always satisfies<br />

equation (4.1)<br />

f*(n*)=C* (4.1)<br />

where C* is the cheapest cost from s to Γ.

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