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Representation. A farmer wants to move himself, a hunrgry silver fox, a hungry, fat goose, and a sack of tasty grain across a river. Unfortunately, his boat is so tiny he can move only one of his possessions across on any trip. What is he to do?. Fox, Farmer, Goose, Grain.

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representation
Representation
  • A farmer wants to move himself, a hunrgry silver fox, a hungry, fat goose, and a sack of tasty grain across a river. Unfortunately, his boat is so tiny he can move only one of his possessions across on any trip. What is he to do?
fox farmer goose grain
Fox, Farmer, Goose, Grain
  • 5 minute break for solving the problem
  • Keep track of how you solve the problem (think about how you think to solve the problem)
representation3
Representation
  • Look at the representation in figure 2.1.
  • Graph like representation
  • Nodes: A safe distribution of entities on both banks of the river
  • Edges: connect nodes separated by a single boat trip
  • Solution: draw a line from start state to end state
analysis
Analysis
  • How many nodes?
  • How many safe nodes?
  • How many links?
  • How many legal links?
representation is key
Representation is key
  • Node/Link representation is good
  • Once represented using nodes and links, problem is simple to solve
representation6
Representation
  • A lexical part: What symbols are allowed in your vocabulary/lexicon
  • A structural part: constraints on how symbols can be arranged
  • A procedural part: access procedures to create, modify descriptions
  • A semantic part: associates meaning with description
semantic nets
Semantic Nets
  • Lexical: Nodes, links, and app-specific link labels
  • Structural: Each link connects a tail node to a head node
  • Semantic: Nodes and links denote application specific entities
  • Procedural: node, link constructors, readers/visitors to traverse the net
good representations
Good Representations
  • Example of a good representation in object identification
  • Identify an object as belonging to a class
  • Basic Method: Describe and Match
    • Describe Object (using a “good” representation)
    • Match to library of object descriptions
    • Return closest match
object identification
Object Identification
  • Feature based object identification
    • Feature extractor, extracts easily identifiable object features (area, perimeter, hole count, hole area, …)
    • Values of these features locate the object in an n-dimensional feature space (an object occupies a feature point in feature space)
    • Compare the distance of unknown object’s feature point to library of known (idealized) object’s feature points. The most likely identity is determined by smallest distance.
administrivia
Administrivia
  • Read Chapters 1 and 2
  • Assignment 1 considers Missionaries and Cannibals is available, due Feb 4.
  • Back of book contains hints
  • Need help, talk to me
3 missionaries 3 cannibals
3 Missionaries 3 Cannibals
  • Three cannibals and three missionaries are standing on the west bank of a river. A boat is available that will hold either one or two people. If the missionaries are ever outnumbered -- on either bank or in the boat -- the cannibals will eat them. Your job is to design a program (come up with a representation and implement a search algorithm) that will get everyone across the river to the east bank safely.
burglar and combination lock
Burglar and combination lock
  • Generate a combination
  • Test if it opens the safe
  • Consider 6 digit combination
    • 10^6 combinations
    • 10^6/2 combinations on average to find correct combination, 3/min  16, 24 hr weeks
generate and test
Generate and Test
  • Powerful problem solving method
  • Until a satisfactory solution is found or no more solutions can be generated
    • Generate the candidate solution
    • Test the candidate solution
  • If an acceptable solution is found, announce it; otherwise announce failure
dendral
Dendral
  • Good generator – complete, nonredundant, only generates structures arising from known formula
  • Tester – Spectrogram comparator
terminology
Terminology
  • State (of a system): Description of a system that is sufficient to determine the future
  • State space: Each node denotes a state, and each link denotes a possible one-step transition from one state to another
state space
State Space
  • A state space is a representation
    • That is a semantic net
    • In which
      • Nodes denote states
      • Links denote transitions between states
  • Initial state, current state, goal state
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