1 Genetic Algorithms. CS 561, Session 26 2 The Traditional Approach Ask an expert Adapt existing designs Trial and error.

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Genetic Algorithms

CS 561, Session 26 2

The Traditional Approach

• Ask an expert• Adapt existing designs• Trial and error

CS 561, Session 26 3

Nature’s Starting Point

Alison Everitt’s “A User’s Guide to Men”

CS 561, Session 26 4

Optimised Man!

CS 561, Session 26 5

Example: Pursuit and Evasion

• Using NNs and Genetic algorithm• 0 learning• 200 tries• 999 tries

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Comparisons

• Traditional• best guess

• may lead to local, not global optimum

• Nature• population of guesses

• more likely to find a better solution

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More Comparisons

• Nature• not very efficient

• at least a 20 year wait between generations• not all mating combinations possible

• Genetic algorithm• efficient and fast

• optimization complete in a matter of minutes• mating combinations governed only by “fitness”

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The Genetic Algorithm Approach

• Define limits of variable parameters• Generate a random population of designs• Assess “fitness” of designs• Mate selection• Crossover• Mutation• Reassess fitness of new population

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A “Population”

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Ranking by Fitness:

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Mate Selection: Fittest are copied and replaced less-fit

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Mate Selection Roulette:Increasing the likelihood but not guaranteeing the fittest reproduction

11%

38%

7%

16%0%

3%

25%

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Crossover:Exchanging information through some part of information (representation)

CS 561, Session 26 14

Mutation: Random change of binary digits from 0 to 1 and vice versa (to avoid local minima)

CS 561, Session 26 15

Best Design

CS 561, Session 26 16

The GA Cycle

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Genetic Algorithms

Adv:

•Good to find a region of solution including the optimal solution. But slow in giving the optimal solution

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Genetic Approach

•When applied to strings of genes, the approaches are classified as genetic algorithms (GA)

•When applied to pieces of executable programs, the approaches are classified as genetic programming (GP)

•GP operates at a higher level of abstraction than GA

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Example: Karl Sim’s creatures

• Creatures• Sea Horse• Snake

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Typical “Chromosome”