GA Exercise (first look)

Click to run World: GA (Finnegans Wake) at Ancient Brain.

• Exercise: Clone and Edit this World.

• Change the speed. See the "frameRate" line.
• It seems we can do frameRate less than 1. (One frame every n seconds.) This appears to be undocumented.

Search for longer strings

• Make target string very long.
• Does search time increase linearly? (Twice as long string takes twice as long to find)

Search for shorter strings

• Change target string to:
  • "hello"
  • "hi"
  • "h"
• You might be surprised what happens. Slow down frameRate to see.

Initial strings

• randomChar() is called by initialisation (initial strings) and mutation.
• Change where the strings are initialised to use character "c" instead of randomChar().
• So every character in every initial string is "c".
• What happens?
• Slow it down to see.

Mutation

• Change mutation to just give character "c".
• Both mutation and crossover are now useless. Why?

• Change mutation to just give character "d".
• What happens?

• Note string is: "riverrun, past Eve and Adam's, from swerve of shore to bend of bay"
• So string all "c" has fitness 0.
• String all "d" has fitness 3.

---

GAs are not for problems where you know the answer

• It should be said that GAs are not for problems where you know the answer.
• If you know the answer there is no need for any search!
• A GA is for a problem where the answer is not known but there is still a measure of "fitness".
• This kind of example (with a known answer) is used to show and debug how the GA works.