SP10 cs188 lecture 3 -- a-star search (2PP)

SP10 cs188 lecture 3 -- a-star search (2PP) - CS 188:...

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1 CS 188: Artificial Intelligence Fall 2009 Lecture 3: A* Search 9/3/2009 Pieter Abbeel – UC Berkeley Many slides from Dan Klein Announcements s Assignments: s Project 0 (Python tutorial): due Thursday 1/28 s Written 1 (Search): due Thursday 1/28 s Project 1 (Search): to be released today, due Thursday 2/4 s You don’t need to submit answers to P1 discussion questions s 5 slip days for projects; up to two per deadline s Try pair programming, not divide-and-conquer s Study materials s Slides, Section materials, Assignments s Book
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2 Office hours, Section s Drop-in lab times: Wed 1/26 4-5pm in 271 Soda s Office hours posted on the course website s Sections starting this week: s Working though exercises are key for your understanding s Section handout contains several exercises similar to written 1 s Solutions will be posted Wed 1pm (after last section) s Section 101: Tue 3-4pm s Section 104: Tue 4-5pm s Section 102: Wed 11-noon s Section 103: Wed noon-1pm Today s Iterative deepening s Uniform cost search s A* Search s Heuristic Design
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3 Recap: Search s Search problem: s States (configurations of the world) s Successor function: a function from states to lists of (state, action, cost) triples; drawn as a graph s Start state and goal test s Search tree: s Nodes: represent plans for reaching states s Plans have costs (sum of action costs) s Search Algorithm: s Systematically builds a search tree s Chooses an ordering of the fringe (unexplored nodes) DFS DFS and BFS Algorithm Complete Optimal Time Space DFS w/ Path Checking BFS Y N O( b m ) O( bm ) b 1 node b nodes b 2 nodes b m nodes s tiers Y N* O( b s+1 ) O( b s+1 ) b s nodes BFS m tiers
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4 Iterative Deepening Iterative deepening uses DFS as a subroutine: 1. Do a DFS which only searches for paths of length 1 or less. 2. If “1” failed, do a DFS which only searches paths of length 2 or less. 3. If “2” failed, do a DFS which only searches paths
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This note was uploaded on 03/01/2010 for the course COMPUTER S 188 taught by Professor Abbel during the Spring '10 term at University of California, Berkeley.

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SP10 cs188 lecture 3 -- a-star search (2PP) - CS 188:...

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