CSE 4705 Artificial Intelligence Jinbo Bi Department of Computer Science & Engineering http://www.engr.uconn.edu/~jinbo

Informed search strategies

Informed search Part I (classical search) Informed = use problem-specific knowledge Best-first search and its variants A* - Optimal search using knowledge Proof of optimality of A* A* for maneuvering AI agents in games Heuristic functions Part II (beyond classical search, Chap 4) Local search and optimization Local search in continuous space Hill climbing, local bean search, …

Informed search Is Uniform cost search the best we can do?

A better idea

The straight-line distance from each city to Bucharest: Start Goal

A heuristic function

Breadth first for games, robots http://theory.stanford.edu/~amitp/GameProgramming/

An optimal informed search (A*)

Breadth first for a world with obstacles Pink: start node; Dark blue: goal Breadth-first search expands many nodes

Informed search (A*) in that world

Greedy best-first search

Greedy best-first search example

Greedy best-first search example

Greedy best-first search example

Greedy best-first search example

Properties of greedy best-first search

Properties of greedy best-first search

Properties of greedy best-first search

A* search

Admissible heuristics

A* search example

A* search example

A* search example

A* search example

A* search example

A* search example

A* search example

Optimality of A* (intuitive)

Optimality of A* using tree search

Optimality of A* using tree search

Properties of A* search

Properties of A* search

Properties of A* search

Properties of A* search

A lemma: Consistency

Creating good heuristic functions Chap 3.6

Heuristic functions

Heuristic functions

Admissible heuristics

Admissible heuristics 8 3+1+2+3+2+2+2+3=18

Relaxed problems

Defining heuristics: h(n)

Dominance

Iterative deepening A* and beyond

Iterative deepening A* and beyond

Informed search II When A* fails – hill climbing, simulated annealing Genetic algorithms

Outline

Local search and optimization

Hill climbing

Hill climbing on a surface of states

Hill climbing search

Hill climbing search example 4

Questions?