CS 480 Lec 2 Sept 4

• complete the introduction

• Chapter 3 (search)

The party example

• If Alex goes, then Beki goes: A B• If Chris goes, then Alex goes: C A• Beki does not go: not B• Chris goes: C

Query: Is it possible to satisfy all these conditions?

This is called satisfiability problem.

Example of languages

• Programming languages:– Formal languages, not ambiguous, but cannot

express partial information. Not expressive enough.• Natural languages:

– Very expressive but ambiguous: ex: small dogs and cats.

• Good representation language:– Both formal and can express partial information, can

accommodate inference• Main approach used in AI: Logic-based languages.

• Predicate-logic with Horn clauses

Deduction algorithms

Example: Given P R, and Q ~R

Can we deduce ~(P & Q)?

Applications

• expert systems (Mycin, dendral are early examples)

• logic programming

• automatic theorem proving (software validation)

Resolution strategy (Robinson)

Example:

X (Y ((mother(X) child_of(Y,X)) loves(X,Y)))mother(mary)child_of(tom,mary)

Can we deduce?

loves(mary, tom)

Resolution strategy of Robinson also works for predicate logic.

But the time complexity is very high.

Logical deduction in predicate logic

techniques• Probabilistic approach to AIKnowledge representation models uncertainties.Example:• H = “Have a headache”• F = “Coming down with Flu”• P(H) = 1/10• P(F) = 1/40• P(H|F) = ½Given that you have a headache, what is the probability that you

have flu?

This kind of modeling is widely used in various prediction problems, e.g., in determining the insurance premium for car etc.

Probabilistic approach to AI

Some games are inherently probabilistic.

•Financial markets

• backgammon

techniques

Training set

New applicant: (young, has job, does not own house, good credit).

Will (s)he default? We can build a probabilistic model to answer.

Classification model – decision tree, Naïve Bayes

Bayesian network

techniques

Machine learning approach to AI:• self-improving algorithms• solution obtained without explicit programming• Closer to modeling human intelligence or natural

intelligence (we learn many things by observing even if step by step procedure absent)

Prominent examples:• Neural networks• Genetic algorithms, evolutionary method

techniques

Neuron (very roughly modeled by neurons in brain)

What a single neuron can and can’t classify?

Using 2 neurons, we can classify the right.

techniques

An algorithm called back propagation algorithm is used to adjust the weights of neurons based on the discrepancy between correct output and computed output.

techniques

Evolutionary algorithms:

• encoding of the collection of solutions as strings.

• goal is to evolve the “best” solution.

• use cross-over and mutation and iterate.

Example of cross-over and mutation

AI prehistory

• Philosophy Logic, methods of reasoning, mind as physical system foundations of learning, language,

rationality• Mathematics Formal representation and proof algorithms,

computation, (un)decidability, (in)tractability,probability

• Economics utility, decision theory • Neuroscience physical substrate for mental activity• Psychology phenomena of perception and motor control,

experimental techniques• Computer building fast computers

engineering• Control theory design systems that maximize an objective

function over time • Linguistics knowledge representation, grammar

Abridged history of AI• 1943 McCulloch & Pitts: Boolean circuit model of

brain• 1950 Turing's "Computing Machinery and

Intelligence"• 1956 Dartmouth meeting: "Artificial Intelligence"

adopted• 1950s Early AI programs, including Samuel's checkers

program, Newell & Simon's Logic Theorist, Gelernter's Geometry Engine

• 1965 Robinson's complete algorithm for logical reasoning (resolution technique)

• 1966—73 AI discovers computational complexityNeural network research almost disappears

• 1969—79 Early development of knowledge-based systems• 1980-- AI becomes an industry • 1986-- Neural networks return to popularity• 1987-- probabilistic techniques dominate• 1995-- major advances in natural languages, web

applications

State of the art• Deep Blue defeated the reigning world chess champion Garry

Kasparov in 1997

• Proved a mathematical conjecture (Robbins conjecture) unsolved for decades

• No hands across America (driving autonomously 98% of the time from Pittsburgh to San Diego)

• During the 1991 Gulf War, US forces deployed an AI logistics planning and scheduling program that involved up to 50,000 vehicles, cargo, and people

• NASA's on-board autonomous planning program controlled the scheduling of operations for a spacecraft

• Proverb solves crossword puzzles better than most humans