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Search 5 주강의. Generating action sequences Generating a new set of states  expanding the state Search strategy ::: the choice of which state to expand.

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Presentation on theme: "Search 5 주강의. Generating action sequences Generating a new set of states  expanding the state Search strategy ::: the choice of which state to expand."— Presentation transcript:

1 Search 5 주강의

2 Generating action sequences Generating a new set of states  expanding the state Search strategy ::: the choice of which state to expand first Search tree, Search graph Data structures for search trees : Queue, Stack

3 Search Strategies Completeness ::: guaranteeing to find a solution where there is one Time complexity Space complexity Optimality ::: to find the high quality solution ???

4 Search Strategies Uninformed (blind) search Informed (heuristic) search

5 Uninformed search I Breadth-first search : branching factor : memory requirement Uniform cost search : g(n). data structure : g(n) = depth(n)  breadth-first search

6 Uninformed search II Depth-first search : stack : ??? completeness  w+1 Depth limit search Iterative deepening search ::: depth 를 증가하면서 depth limit search Bi-directional Search

7 숙제 ( 기간 :: 10 월 24 일까지 ) Missionary-cannibals 문제에 대해 (1) depth-first search 로는 답을 구하지 못할 수 있음을 보여라 (2) depth-first search 에 같은 sate 가 다시 나타나면 제거하는 기능이 있으면 답을 구할 수 있다. 이를 프로그램하라. (3) breadth-first search 로 구현하라. (4) iterative deepening 방법으로 구현하라. (5) (2), (3), (4) 에 대해 space 와 수행속도를 비교하라

8 Comparing Search Strategies Criterion Breadth- first Uniform -cost Depth- first Depth- Limited Iterative Deepening Bidirect ional Timebdbd b d bmbm blbl bdbd B d/2 Spacebdbd bdbd bmblbdB d/2 Optimalyes no yes Completeyes noYes, If ≥d yes B: branching factor, d: depth of solution, m: maximum depth, l: depth limit

9 Constraint Satisfaction Search The states are defined by the values of a set of variables and the goal test specifies a set of constraints that must the values must obey Cryptarithmetic, 8 queens problem, VLSI design In CSP, the goal test is decomposed into a set of constraints on variables rather than being a blackbox

10 Search in CSP Depth-first search on a CSP wastes time searching when constraints have already been violated Backtracking search Forward checking ::: Each time a variable is instantiated, forward checking deletes from the domains of the as-yet-uninstantiated variables all of those values that conflict with the variables assigned Constraints propagation

11 숙제 문제 3.2, 3.3, 3.5, 3.8, 3.11, 3.13, 3.14, 3.17, 3.20, 3.21


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