1. Data Mining CS 341, Spring 2007 Genetic Algorithm

2. © Prentice Hall2 Genetic Algorithms Optimization search type algorithms. Optimization search type algorithms. Creates an initial feasible solution and iteratively creates new “better” solutions. Creates an initial feasible solution and iteratively creates new “better” solutions. Based on human evolution and survival of the fittest. Based on human evolution and survival of the fittest. Must represent a solution as an individual. Must represent a solution as an individual. Individual: string I=I 1,I 2,…,I n where I j is in given alphabet A. Individual: string I=I 1,I 2,…,I n where I j is in given alphabet A. Each character I j is called a gene. Each character I j is called a gene. Population: set of individuals. Population: set of individuals.

3. © Prentice Hall3 Genetic Algorithms A Genetic Algorithm (GA) is a computational model consisting of five parts: A Genetic Algorithm (GA) is a computational model consisting of five parts: –A starting set of individuals, P. –Crossover: technique to combine two parents to create offspring. –Mutation: randomly change an individual. –Fitness: determine the best individuals. –Algorithm which applies the crossover and mutation techniques to P iteratively using the fitness function to determine the best individuals in P to keep.

4. © Prentice Hall4 Crossover Examples

5. © Prentice Hall5 Genetic Algorithm

6. © Prentice Hall6 GA Advantages/Disadvantages Advantages Advantages –Easily parallelized Disadvantages Disadvantages –Difficult to understand and explain to end users. –Abstraction of the problem and method to represent individuals is quite difficult. –Determining fitness function is difficult. –Determining how to perform crossover and mutation is difficult.

7. © Prentice Hall7 Genetic Algorithm Example { A,B,C,D,E,F,G,H} { A,B,C,D,E,F,G,H} Randomly choose initial solution: Randomly choose initial solution: {A,C,E} {B,F} {D,G,H} or 10101000, 01000100, 00010011 Suppose crossover at point four and choose 1 st and 3 rd individuals: Suppose crossover at point four and choose 1 st and 3 rd individuals: 10100011, 01000100, 00011000 What should termination criteria be? What should termination criteria be?

8. © Prentice Hall8 GA Algorithm