Lecture-4

Lecture-4 - Artificial Intelligence CS 165A 165A Friday,...

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Artificial Intelligence S 165A CS 165A Friday, Jan 14, 2011 asic Search (Ch 3) Basic Search (Ch. 3) 1
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Notes • Lecture notes – Username: cs165a – Password: winter2011 • Homework 1 due by Thursday 2 pm. 2
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Review • Problem formulation and search – State-space description < {S}, S , {S }, {O}, {g} > 0 G S : Possible states S 0 : Initial state of the agent Goal state(s) S G : Goal state(s) – Or equivalently, a goal test G(S) O : Operators O: {S} => {S} – Describes the possible actions of the agent g : Path cost function, assigns a cost to a path/action ninformed (blind) search Uninformed (blind) search – Is this a goal state or not? – Know current path cost (from start to current node) 3 – No information about the “goodness” of a state • What are we about to do right now?
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Example: MU-Puzzle States: Strings comprising the letters M, I, and U itial state: MI Initial state: MI Goal state: MU •O perators: (where x stands for any string, including the null string ) 1. x I x IU “Append U” 2. M x M x x Replicate x 3. x I I I x “Replace III with U” M I M I I y U y pU 4. x UU y xy “Drop UU” ath cost: one per step M I I I I M U I M U I U UIUUIU Path cost: one per step •T r y i t Can you draw the state-space diagram? M U I U U I U M U I U U I U U I U U I U 4 Are you guaranteed a solution?
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Clarification of the MU-puzzle rules: 1. If the string ends with I you may add U; for example, MI becomes MIU 2. If the string is Mx then you may create Mxx; for example, MI becomes MII; MIU becomes MIUIU 3. If the string contains III you may replace those three characters with U 4. If the string contains UU you may eliminate both characters 5
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Example: The Vacuum World • Simplified world: 2 grids States: Location of vacuum, dirt in grids Operators: Move left, move right, suck dirt Goal test: Grids free of dirt Path cost: Each action costs 1 How many states for n squares? 6
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The Vacuum World (cont.) • How to reach the goal? – If starting at top left state: S, R, S – If starting at middle far right state: L, S • What if agent doesn’t know its initial state? – You probably need to redraw the state diagram! epresent initial uncertainty as one “meta ate” or elief ate – Represent initial uncertainty as one meta-state or belief-state. For example… Can coerce the world into a goal state – Example of vacuum cleaner Size of belief-state space? 7
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The Vacuum World (cont.) 8
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Example: Measuring Problem 3 5 9 • You have three empty buckets – 3 gallon bucket gallon bucket 5 gallon bucket – 9 gallon bucket • You can fill buckets to the top and you can empty buckets onto the ground or into other buckets • Task: Measure out 7 gallons of water in fewest # of steps tates initial state operators goal test path cost?
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This note was uploaded on 02/22/2011 for the course CS 165A taught by Professor Su during the Spring '11 term at UCSB.

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Lecture-4 - Artificial Intelligence CS 165A 165A Friday,...

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