Genetic Algorithms Sushil J. Louis Evolutionary Computing Systems LAB Dept. of Computer Science University of Nevada, Reno

2 Search techniques Hill Climbing/Gradient Descent –You are getting closer OR You are getting further away from correct combination –Quicker –Distance metric could be misleading –Local hills

3 Search techniques Parallel hillclimbing –Everyone has a different starting point –Perhaps not everyone will be stuck at a local optima –More robust, perhaps quicker

4 Genetic Algorithms Parallel hillclimbing with information exchange among candidate solutions Population of candidate solutions Crossover for information exchange Good across a variety of problem domains

5 Genetic Algorithm Generate pop(0) Evaluate pop(0) T=0 While (not converged) do –Select pop(T+1) from pop(T) –Recombine pop(T+1) –Evaluate pop(T+1) –T = T + 1 Done

6 Evaluate Decoded individual Fitness Application dependent fitness function

7 Designing a parity checker Search for circuit that performs parity checking Parity: if even number of 1s in input correct output is 0, else output is 1 Important for computer memory and data communication chips What is the genotype? – selected, crossed over and mutated A circuit is the phenotype – evaluated for fitness. How do you construct a phenotype from a genotype to evaluate?

8 What is a genotype? A genotype is a bit string that codes for a phenotype Randomly chosen crossover point CrossoverParentsOffspring Mutation Randomly chosen mutation point

9 Genotype to Phenotype mapping length binary string row of 150 becomes 6 rows of 25

10 Genotype to Phenotype mapping A circuit is made of logic gates. Receives input from the 1 st column and we check output at last column Each group of five bits codes for one of 16 possible gates and the location of second input

11 Evaluating the phenotype Feed the gate an input combination Check whether the output produced by a decoded member of the population is correct Give one point for each correct output This is essentially a circuit simulation Max Fitness = 2^6 = 64

12 Circuits Parity Checker Adder

13 Traveling Salesperson Problem Find a shortest length tour of N cities N! possible tours 10! = ! = Chip layout, truck routing, logistics

14 Predicting subsurface structure Find subsurface structure that agrees with experimental observations Mining, oil exploration, swimming pools

15 Designing a truss Find a truss configuration that minimizes vibration, minimizes weight, and maximizes stiffness.

16 How does it work Sum Avg Max String decoded f(x^2) fi/Sum(fi) Expected Actual

17 How does it work cont’d 0110| | | | Sum1754 Avg439 Max729 String mate offspring decoded f(x^2)