1 artificial intelligence an introductory course

1

Artificial Intelligence

An Introductory Course

2

Outline

1. Introduction

2. Problems and Search

3. Knowledge Representation

4. Advanced Topics

- Game Playing

- Uncertainty and Imprecision

- Planning

- Machine Learning

3

References

• Artificial Intelligence (1991)Elaine Rich & Kevin Knight, Second Ed, Tata McGraw Hill

• Decision Support Systems and Intelligent SystemsTurban and Aronson, Sixth Ed, PHI

4

Introduction

• What is AI?

• The foundations of AI

• A brief history of AI

• The state of the art

• Introductory problems

5

What is AI?

6

What is AI?

• Intelligence: “ability to learn, understand and think” (Oxford dictionary)

• AI is the study of how to make computers make things which at the moment people do better.

• Examples: Speech recognition, Smell, Face, Object, Intuition, Inferencing, Learning new skills, Decision making, Abstract thinking

7

What is AI?

Thinking humanly Thinking rationally

Acting humanly Acting rationally

8

Acting Humanly: The Turing Test

• Alan Turing (1912-1954)

• “Computing Machinery and Intelligence”

(1950)

Human Interrogator

Human

AI System

Imitation Game

9

Acting Humanly: The Turing Test

• Predicted that by 2000, a machine might have a 30% chance of fooling a lay person for 5 minutes.

• Anticipated all major arguments against AI infollowing 50 years.

• Suggested major components of AI: knowledge, reasoning, language, understanding, learning.

10

Thinking Humanly: Cognitive Modelling

• Not content to have a program correctly solving a problem.

More concerned with comparing its reasoning

steps to traces of human solving the same problem.

• Requires testable theories of the workings of the human mind: cognitive science.

11

Thinking Rationally: Laws of Thought

• Aristotle was one of the first to attempt to codify “right thinking”, i.e., irrefutable reasoning processes.

• Formal logic provides a precise notation and rules for representing and reasoning with all kinds of things in the world.

• Obstacles:- Informal knowledge representation.

- Computational complexity and resources.

12

Acting Rationally

• Acting so as to achieve one’s goals, given one’s beliefs.

• Does not necessarily involve thinking.

• Advantages:- More general than the “laws of thought”

approach.- More amenable to scientific development than

human- based approaches.

13

The Foundations of AI

• Philosophy (423 BC - present):- Logic, methods of reasoning.

- Mind as a physical system.- Foundations of learning, language, and

rationality.

• Mathematics (c.800 - present):- Formal representation and proof.

- Algorithms, computation, decidability, tractability.

- Probability.

14

The Foundations of AI

• Psychology (1879 - present):- Adaptation.

- Phenomena of perception and motor control.- Experimental techniques.

• Linguistics (1957 - present):- Knowledge representation.

- Grammar.

15

A Brief History of AI

• The gestation of AI (1943 - 1956):- 1943: McCulloch & Pitts: Boolean circuit model

of brain.- 1950: Turing’s “Computing Machinery and

Intelligence”.- 1956: McCarthy’s name “Artificial Intelligence”

adopted.

• Early enthusiasm, great expectations (1952 - 1969):

- Early successful AI programs: Samuel’s checkers,

Newell & Simon’s Logic Theorist, Gelernter’s Geometry

Theorem Prover.- Robinson’s complete algorithm for logical

reasoning.

16


• A dose of reality (1966 - 1974):- AI discovered computational complexity.

- Neural network research almost disappeared after

Minsky & Papert’s book in 1969.

• Knowledge-based systems (1969 - 1979):- 1969: DENDRAL by Buchanan et al..

- 1976: MYCIN by Shortliffle.- 1979: PROSPECTOR by Duda et al..

17


• AI becomes an industry (1980 - 1988):- Expert systems industry booms.

- 1981: Japan’s 10-year Fifth Generation project.

• The return of NNs and novel AI (1986 - present):- Mid 80’s: Back-propagation learning algorithm

reinvented.- Expert systems industry busts.- 1988: Resurgence of probability.- 1988: Novel AI (ALife, GAs, Soft Computing, …).- 1995: Agents everywhere.- 2003: Human-level AI back on the agenda.

18

Task Domains of AI• Mundane Tasks:

– Perception• Vision• Speech

– Natural Languages• Understanding• Generation• Translation

– Common sense reasoning– Robot Control

• Formal Tasks– Games : chess, checkers etc– Mathematics: Geometry, logic,Proving properties of programs

• Expert Tasks:– Engineering ( Design, Fault finding, Manufacturing planning)– Scientific Analysis– Medical Diagnosis– Financial Analysis

19

AI Technique

• Intelligence requires Knowledge• Knowledge posesses less desirable properties such as:

– Voluminous– Hard to characterize accurately– Constantly changing– Differs from data that can be used

• AI technique is a method that exploits knowledge that should be represented in such a way that:– Knowledge captures generalization– It can be understood by people who must provide it– It can be easily modified to correct errors.– It can be used in variety of situations

20

The State of the Art

• Computer beats human in a chess game.

• Computer-human conversation using speech

recognition.

• Expert system controls a spacecraft.

• Robot can walk on stairs and hold a cup of

water.

• Language translation for webpages.

• Home appliances use fuzzy logic.

• ......

21

Tic Tac Toe

• Three programs are presented :– Series increase– Their complexity– Use of generalization– Clarity of their knowledge– Extensability of their approach

22

Introductory Problem: Tic-Tac-Toe

X X o

23


Program 1:Data Structures: • Board: 9 element vector representing the board, with 1-9 for

each square. An element contains the value 0 if it is blank, 1 if it is filled by X, or 2 if it is filled with a O

• Movetable: A large vector of 19,683 elements ( 3^9), each element is 9-element vector.

Algorithm:

1. View the vector as a ternary number. Convert it to a decimal number.

2. Use the computed number as an index into Move-Table and access the vector stored there.

3. Set the new board to that vector.

24


Comments:This program is very efficient in time.

1. A lot of space to store the Move-Table.

2. A lot of work to specify all the entries in the Move-Table.

3. Difficult to extend.

25


1 2 3 4 5 6 7 8 9

26

Introductory Problem: Tic-Tac-ToeProgram 2:Data Structure: A nine element vector representing the board.

But instead of using 0,1 and 2 in each element, we store 2 for blank, 3 for X and 5 for O

Functions:Make2: returns 5 if the center sqaure is blank. Else any other

balnk sqPosswin(p): Returns 0 if the player p cannot win on his next

move; otherwise it returns the number of the square that constitutes a winning move. If the product is 18 (3x3x2), then X can win. If the product is 50 ( 5x5x2) then O can win.

Go(n): Makes a move in the square n

Strategy:

Turn = 1 Go(1)Turn = 2 If Board[5] is blank, Go(5), else Go(1)Turn = 3 If Board[9] is blank, Go(9), else Go(3)Turn = 4 If Posswin(X) 0, then Go(Posswin(X)).......

27


Comments:

1. Not efficient in time, as it has to check several conditions before making each move.

2. Easier to understand the program’s strategy.

3. Hard to generalize.

28


8 3 4 1 5 9 6 7 2

15 - (8 + 5)

29


Comments:

1. Checking for a possible win is quicker.

2. Human finds the row-scan approach easier, whilecomputer finds the number-counting approach moreefficient.

30


Program 3:

1. If it is a win, give it the highest rating.

2. Otherwise, consider all the moves the opponent could make next. Assume the opponent will make the move that is worst for us. Assign the rating of that move to the current node.

3. The best node is then the one with the highest rating.

31


Comments:

1. Require much more time to consider all possible moves.

2. Could be extended to handle more complicated games.

32

Exercises

1. Characterize the definitions of AI:

"The exciting new effort to make computers think ... machines with minds, in the full and literal senses" (Haugeland, 1985)

"[The automation of] activities that we associate with human thinking, activities such as decision-making, problem solving, learning ..." (Bellman, 1978)

33

Exercises

"The study of mental faculties, through the use of computational models" (Charniak and McDermott, 1985)

"The study of the computations that make it possible to perceive, reason, and act" (Winston, 1992)

"The art of creating machines that perform functions that require intelligence when performed by people" (Kurzweil, 1990)

34

Exercises

"The study of how to make computers do things at which, at the moment, people are better" (Rich and Knight, 1991)

"A field of study that seeks to explain and emulate intelligent behavior in terms of computationl processes" (Schalkoff, 1990)

"The branch of computer science that is concerned with the automation of intelligent behaviour" (Luger and Stubblefield, 1993)

35

Exercises

"A collection of algorithms that are computationally tractable, adequate approximations of intractabiliy specified problems" (Partridge, 1991)

"The enterprise of constructing a physical symbol system that can reliably pass the Turing test" (Ginsberge, 1993)

"The f ield of computer science that studies how machines can be made to act intelligently" (Jackson, 1986)

1 artificial intelligence an introductory course

Documents