# AI News, Artificial Intelligence/Search/Heuristic search/Astar Search

- On Wednesday, October 3, 2018
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## Artificial Intelligence/Search/Heuristic search/Astar Search

When there is a formulated search problem, a set of states, a set of operators, an initial state, and a goal criterion we can use search techniques to solve the problem (Pearl &

search algorithm is explained in simple terms by Cawsey (1998): Suppose that you are trying to find your way around in a small town, which has many one way streets.

There might be much inconvenience in the whole picture: Once you have passed though one street you may not be able to go back, as it is one way, or you may be stuck in a park.

In small scale search problems, as introduced above, simple search techniques are sufficient to do systematic search.

Heuristic search makes use of the fact that most problem spaces provide some information that distinguishes among states in terms of their likelihood of leading to a goal.

For instance, if there are two options to chose from, one of which is a long way from the initial point but has a slightly shorter estimate of distance to the goal, and another that is very close to the initial state but has a slightly longer estimate of distance to the goal, best-first search will always choose to expand next the state with the shorter estimate.

In short, the A* algorithm searches all possible routes from a starting point until it finds the shortest path or cheapest cost to a goal.

f(n) is the total search cost, g(n) is actual lowest cost( shortest distance traveled) of the path from initial start point to the node n, h(n) is the estimated of cost of cheapest(distance) from the node n to a goal node.

At each node, the lowest f value is chosen to be the next step to expand until the goal node is chosen and reached for expansion.

search strategy is convergent if it promises to find a path, a solution graph, or information on whether they exist (Bolc &

A* is the most popular choice for path finding, because it's fairly flexible and can be used in a wide range of contexts such as games (8-puzzle and a path finder).

- On Sunday, March 24, 2019

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