# HPSLec12-2010 - Lecture#12 Human Problem Solving I II...

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Lecture #12 Human Problem Solving AGENDA I. Structure of Move Problems II. Ways of Cutting Down the Possibilities A. Sub-goals B. Working Backward C. Macroactions & Microactions III. Specific Search Strategies IV. The General Problem Solver A. Production Systems B. Anderson’s ACT*, ACT-R V. Brains versus Digital Computers VI. Brain Teasers Involving Time

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I. Structure of Move Problems The original efforts at machine problem solving, namely the General Problem Solver (GPS) of Newell and Simon, were aimed at ‘move problems’. Here is a very simple example I will work with. A father and his two sons reach the bank of a treacherous river. They have a boat that can hold 200 LB. The father weighs 200 LB and each of the boys weigh 100 LB. All are capable of piloting the boat. Can they get across safely? For any such move problem, we need to specify three things:
Specifying the Boat Problem The set up: F S 1 S 2 Boat Treacherous River (1)Starting State (2) Goal State F S 1 S 2 (3) Allowable operations . One or more folks pile into the boat and head off on the other side. These three components generate the ‘basic problem space’.

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Basic Problem Space Notation is important. I will use [xIy], where x is a list of things on the left bank and y lists things on the right bank, B for boat. FSSBI .I. All FS SI. FSISB S SSIFB F DEAD ENDS LOOPS FISSB SS This is part of the Basic Problem Space showing Intermediate Problem States , Allowable Operators , Dead Ends, Destructive and Non- Destructive Operators, Inverse Operators and Loops . Etc.
Basic Problem Space (Cont.) FSSBI. .I. All FS SI. SSIFB F FISSB SS FSBIS S SIFSB F .IS FS SSBIF .IFSSB GOAL FSISB S SI. FS START S SOLUTION: FSSBI. FISSB FSBIS SIFSB SSBIF .IFSSB

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Basic Problem Spaces are Mazes The similarity of the basic problem space to a maze is clear. In move problems the basic problem space takes the form of a maze, though there may be several ways to exit the maze, i.e. solve the problem. Of course computers could in principle explore all maze routes and find a solution by brute force. There are two problems with the ‘brute force’ method: (1) There may be even too many possibilities; (2) this method gives no insight into human problem solving. Actually some problems called ‘NP ’ (for non-polynomial ) problems there are principle limitations on brute force- more on this later. People use learned skills in cutting through the ‘maze’ and the goal of Newell and Simon’s GPS was to capture these in a computer problem solver. First we discuss the concepts that humans can use informally.
II. Ways of Cutting Down the Possibilities Many problems have symmetries that cut down the possibilities to consider. Later we will play versions of tic-tat-toe. Suppose you wanted to study the simple game.

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