problem solving •ways of solving problemsmeans-end analysis •problem solving as search –for...
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Problem Solving• Ways of solving problems
– Means-end analysis– Analogy– Brainstorming
• Pitfalls in problem solving– Functional fixedness– Mental set– Wrong representation– Starting at wrong point
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Means-end Analysis• Problem solving as search
– For solving well-defined problem• Start• Goals & Subgoals• Operators - methods for moving from state to state
• Heuristics– Strategies for choosing an operator to apply– Not guaranteed to be correct, but generally helpful
• Hillclimbing– Choose operator that moves closest to the goal– Can get stuck in local maxima - states that are closer to the goal
than any neighboring states, but still are not the goal– Leave local maxima by back-tracking or adding randomness
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Problem solving as search
Start
Goal
AB C
D E
F G
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Heuristics
For solving anagrams like: GAKBNI
Try placing letters together thatoften occur together
For winning tic-tac-toe
Play in the middle
For dating a person met at a coffee house
Ask what they are drinking
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The eight-tiles puzzle
1 24 5 67 8
3
Goal
1 24
5
67 83
Start
Operators: Move space up, down, left, or right
52 3
6
Heuristic: Choose operator that makes moretiles in correct space
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Backtracking
1 24 5
67 8
3 Backtrack by taking back recentmoves and applying new operators5
Stuck at local maximumby hill climbing
Goal = global maximum
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Heuristics
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Problem solving by analogy• Use solved problem to solve new problem• Analogy = Superficial features are different, but
same at a deep level– Solar system and atom
• Analogies are missed unless people are given hintsthat they are related, or multiple related stories
• People are too influenced by superficial similarities– Use word processor commands that were learned with
superficially similar documents (bibliographies, menus)– Decision making is influenced by superficial features
• Does the scenario remind people of Vietnam or WWII?
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Problem Solving by Brainstorming• Generate ideas without critical examination• Useful for ill-defined problems• Creativity with SCAMPER
– Substitute, Combine, Add, Magnify/minify– Place, Eliminate, Reverse/Reorder
• Divergent thinking - explore many possibilities– 100 uses for a brick– Remote associates test
Type Ghost Story WriterFood Catcher Hot DogCanadian Golf Sandwich ClubTug Gravy Show Boat
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People are often too influenced by existing solutions
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Pitfalls of Problem Solving• Functional fixedness
– Tendency to view things in terms of their familiar uses– Two-string problem, candle problem– Better solutions if objects not “pre-utilized”– Young children don’t suffer as much fixedness
• Mental set– Bias to solve problems in a way that has worked in the past– Luchins’ water jugs– Priming of solutions
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Fewer solutions when tools were used (as tools) previously
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Problem: Attach the candle to the wall somehow
Solution: use tacks’ box as a support
More solutions when tacks are outside of box
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Avoid functional fixedness by looking at the world with fresh eyes
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Pitfalls of Problem Solving• Wrong representation
– Experts spend more time figuring out how to represent a problemthan novices (40% compared to 7%)
– The monk problem– The missing dominoes problem
• Starting at the wrong point– Often it is useful to go from goal to start– Choose the starting point that has fewer choice points
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Can 31 dominoes cover the checkerboard with two missing squares?
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Reasoning backwards is helpful if there are more choice points fromstarting point than from goal.