Data commit

Task/Evolutionary-algorithm/Ruby/evolutionary-algorithm.rb

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+@target = "METHINKS IT IS LIKE A WEASEL"
+Charset = [" ", *"A".."Z"]
+COPIES = 100
+
+def random_char; Charset.sample end
+
+def fitness(candidate)
+  sum = 0
+  candidate.chars.zip(@target.chars) {|x,y| sum += (x[0].ord - y[0].ord).abs}
+  100.0 * Math.exp(Float(sum) / -10.0)
+end
+
+def mutation_rate(candidate)
+  1.0 - Math.exp( -(100.0 - fitness(candidate)) / 400.0)
+end
+
+def mutate(parent, rate)
+  parent.each_char.collect {|ch| rand <= rate ? random_char : ch}.join
+end
+
+def log(iteration, rate, parent)
+  puts "%4d %.2f %5.1f %s" % [iteration, rate, fitness(parent), parent]
+end
+
+iteration = 0
+parent = Array.new(@target.length) {random_char}.join
+prev = ""
+
+while parent != @target
+  iteration += 1
+  rate = mutation_rate(parent)
+  if prev != parent
+    log(iteration, rate, parent)
+    prev = parent
+  end
+  copies = [parent] + Array.new(COPIES) {mutate(parent, rate)}
+  parent = copies.max_by {|c| fitness(c)}
+end
+log(iteration, rate, parent)