Document Sample

             B. Ravikumar
      Computer Science Department
           116 I Darwin Hall

              Class meets:
             Fridays 9 to 12
                          Course details
Catalog Description:

A survey of techniques that simulate human intelligence.
Topics may include: pattern recognition, general problem
solving, adversarial game-tree search, decision-making, expert
systems, neural networks, fuzzy logic, and genetic algorithms.
Prerequisite: CS 315 or consent of instructor.

Background Expected:

•Programming and data structures (CS 315)
• Discrete mathematics (CS 242)
•Linear algebra

 Some background in logic and probability will be helpful, but not
                      Course details
Course Goals:

AI covers wide range of topics:

• understanding language
• vision and speech processing
• problem solving, planning
• common sense reasoning.

AI techniques:

• combinatorial (searching, A* algorithm etc.)
• logical        (prove assertion in formal framework)
• probabilistic (decision tree, Bayesian network)
• machine learning (neural network, evolutionary technique)
                      Course details

Other references:

• N. Nillsson, AI: A new synthesis.

• Winston, Artificial Intelligence.
Course details
                             Course details
Short Quizzes (5 – 10%)

Two Mid-Term tests (20%) – Both tests will be in class and will be about 75
miutes long. The tests will be open book/open notes.

Home Work and Projects (40 - 50%) – There will be some common
programming projects and a final project.

The final project will be done individually. You can choose a problem from a
list that will be provided early in the semester. The project is due the last
week of the semester. You are to write a report summarizing your
contributions to the chosen problem. Some selected project work will be
presented in the department colloquium.

Final Examination (25 - 30%) – The final examination will be comprehensive
and will take place at the scheduled time posted in the web page
http://www.sonoma.edu/university /classsched/ finals_sched.pdf (not
updated for Fall 09 as of August 15, 2009.)
                   Lecture 1         Outline

•   Course overview
•   What is AI?
•   A brief history
•   The state of the art

             Slides adapted from Russell and Norvig, AIAMA
                 Course overview
• Introduction (chapters 1,2)
• Combinatorial (search) approach to AI (chapters
• Symbolic (logical) approach to AI (chapters 7,8,9)
• Probabilistic approach to AI (chapters 13,14)
• Learning approach to AI (chapters 18,20)
• Natural Language Processing (chapter 22,23)
• Computer vision (Chapter 24)
                  What is AI?

Authors think AI falls into four categories:

  Thinking humanly Thinking rationally
  Acting humanly   Acting rationally

The textbook advocates "acting rationally"
                      What is AI?

Before attempting a definition, we will state some
major contemporary applications of AI:

• business: advertising, financial decision making
• web: identifying objects in images, social network
models etc.
• medical: image classification (belign vs. malignant
tumor), image analysis using functional MRI
• multiple field: language translation, semantic analysis,
speech synthesis, speech to text conversion.
• industrial: vision, robotics
             Acting humanly: Turing Test

• Turing (1950) "Computing machinery and intelligence":
• "Can machines think?"  "Can machines behave
• Operational test for intelligent behavior: the Imitation Game

• 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 in following 50
• Suggested major components of AI: knowledge, reasoning,
  language understanding, learning
   Thinking humanly: cognitive modeling
• 1960s "cognitive revolution": information-
  processing psychology
• Requires scientific theories of internal activities of
  the brain
• How to validate? Requires
     1) Predicting and testing behavior of human subjects (top-
     down) or
     2) Direct identification from neurological data (bottom-

• Both approaches (roughly, Cognitive Science and
         Thinking rationally: "laws of thought"

•    What are correct arguments/thought processes?
•    Several Greek schools developed various forms of logic:
     notation and rules of derivation for thoughts; may or may
     not have proceeded to the idea of mechanization
•    Direct line through mathematics and philosophy to
     modern AI
•    Problems:
    1.   Not all intelligent behavior is mediated by logical
    2.   What is the purpose of thinking? What thoughts should
         I have?
      Acting rationally: rational agent

• Rational behavior: doing the right thing
• The right thing: that which is expected to maximize
  goal achievement, given the available information
• Doesn't necessarily involve thinking – e.g., blinking
  reflex – but thinking should be in the service of
  rational action
                     AI techniques
•   Combinatorial search problems
    –   state space (over which search is performed)
    –   finite state space (discrete)
    –   how to move from one state to another (transition

•   Applications
    –   Games (one player or two players)
    –   Navigation (robotics)

•   Solution
    –   Search tree exploration
• Combinatorial search approach

                                   1   2   3           1   2   3
Sliding piece puzzle:              4       6           4   5   6
                          Start:               goal:
                                   7   5   8           7   8

Legal moves: slide a piece next to empty slot.

Many AI problems can be modeled as search problems.
A portion of a search tree for the 8-puzzle.
              Combinatorial search

•Uninformed search
     • depth-first
     • breadth-first
     • iterative deepening
     • breadth-depth

• informed search
   • best-first
               Combinatorial search

•Depth-first search

 What are the ways to speed-up DFS?
               Combinatorial search

• Breadth-first search
                Combinatorial search

• heuristic search
 • for each node, a heuristic provides an estimate of its
 distance from the goal.

 • for sliding-piece puzzle, Manhattan distance is one
 such estimate.

 • estimate for other search problems? (e.g. queen
Combinatorial search

                       placement in the
                       5th row.
• Symbolic (logical) approach to AI
intelligent problem solving requires reasoning and

Knowledge is represented as a set of logical
  assertions A1, …, An, and a conclusion to be drawn
  is also expressed as an assertion.

Can we deduce F from A1, …, An?
                    Knowledge bases

• Knowledge base = set of sentences in a formal language

• Declarative approach to building an agent (or other
   – Tell it what it needs to know
• Then it can Ask itself what to do - answers should follow
  from the KB
• Agents can be viewed at the knowledge level
   i.e., what they know, regardless of how implemented
                   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
           Given P  R, and Q  ~R
Example:                                Resolution strategy
           Can we deduce ~(P & Q)?


                     • expert systems (Mycin, dendral are
                     early examples)

                     • logic programming

                     • automatic theorem proving
                     (software validation)
        Logical deduction in predicate logic


X (Y ((mother(X)  child_of(Y,X))  loves(X,Y)))

Can we deduce?

loves(tom, mary)
• Probabilistic approach to AI
Knowledge representation models uncertainties.
• H = “Have a headache”
• F = “Coming down with Flu”
• P(H) = 1/10
• P(F) = 1/40
• P(H|F) = ½
Given 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
              Probabilistic approach to AI

Some games are inherently probabilistic.

   •Financial markets

   • backgammon

                                                  Training set

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

Will (s)he default? We can build a probabilistic model to answer.
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
Neuron (very roughly modeled by neurons in human

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

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
                     AI prehistory

• Philosophy       Logic, methods of reasoning, mind as physical
                   system foundations of learning, language,
• Mathematics      Formal representation and proof algorithms,
                   computation, (un)decidability, (in)tractability,
• Economics        utility, decision theory
• Neuroscience     physical substrate for mental activity
• Psychology       phenomena of perception and motor control,
                   experimental techniques
• Computer         building fast computers
• 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
• 1966—73      AI discovers computational complexity
               Neural network research almost disappears
•   1969—79    Early development of knowledge-based systems
•   1980--     AI becomes an industry
•   1986--     Neural networks return to popularity
•   1987--     AI becomes a science, probabilistic techniques
• 1995--       The emergence of intelligent agents
                     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