mirror of
https://github.com/danth/stylix
synced 2024-11-23 04:33:15 +00:00
ba5565d698
Simplified a lot of code which was unnecessarily generic. Now using monads to manage the state of the random number generator rather than passing it around by hand. Also made some performance improvements, then increased the population size so more combinations are tried in a similar length of time.
127 lines
4.1 KiB
Haskell
127 lines
4.1 KiB
Haskell
{-# LANGUAGE MultiParamTypeClasses #-}
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module Ai.Evolutionary ( Species(..), evolve ) where
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import Data.Ord ( Down(Down), comparing )
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import Data.Vector ( (!) )
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import qualified Data.Vector as V
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import Data.Vector.Algorithms.Intro ( selectBy )
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import System.Random ( randomRIO )
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import Text.Printf ( printf )
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numSurvivors :: Int
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numSurvivors = 500
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numNewborns :: Int
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numNewborns = 50000 - numSurvivors
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mutationProbability :: Double
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mutationProbability = 0.75
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randomFromVector :: V.Vector a -> IO a
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randomFromVector vector = do
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index <- randomRIO (0, V.length vector - 1)
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return $ vector ! index
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{- |
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A genotype is a value which is generated by the genetic algorithm.
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The environment is used to specify the problem for which
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we are trying to find the optimal genotype.
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-}
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class Species environment genotype where
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-- | Randomly generate a new genotype.
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generate :: environment -> IO genotype
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-- | Randomly mutate a single genotype.
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mutate :: environment -> genotype -> IO genotype
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-- | Randomly combine two genotypes.
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crossover :: environment -> genotype -> genotype -> IO genotype
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-- | Score a genotype. Higher numbers are better.
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fitness :: environment -> genotype -> Double
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initialPopulation :: Species e g
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=> e -- ^ Environment
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-> IO (V.Vector g) -- ^ Population
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initialPopulation environment
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= V.replicateM numSurvivors (generate environment)
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-- | Expand a population by crossovers followed by mutations.
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evolvePopulation :: Species e g
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=> e -- ^ Environment
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-> V.Vector g -- ^ Survivors from previous generation
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-> IO (V.Vector g) -- ^ New population
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evolvePopulation environment population = do
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let randomCrossover = do
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a <- randomFromVector population
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b <- randomFromVector population
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crossover environment a b
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randomMutation chromosome = do
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r <- randomRIO (0.0, 1.0)
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if r <= mutationProbability
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then mutate environment chromosome
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else return chromosome
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newborns <- V.replicateM numNewborns randomCrossover
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let nonElites = V.tail population V.++ newborns
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nonElites' <- V.mapM randomMutation nonElites
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return $ V.head population `V.cons` nonElites'
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selectSurvivors :: Species e g
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=> e -- ^ Environment
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-> V.Vector g -- ^ Original population
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-> (Double, V.Vector g) -- ^ Best fitness, survivors
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selectSurvivors environment population =
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let -- Fitness is stored to avoid calculating it for each comparison.
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calculateFitness g = (fitness environment g, g)
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getFitness = fst
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getGenotype = snd
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compareFitness = comparing $ Down . fst
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-- Moves k best genotypes to the front, but doesn't sort them further.
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selectBest k vector = selectBy compareFitness vector k
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selected = V.modify (selectBest 1)
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$ V.take numSurvivors
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$ V.modify (selectBest numSurvivors)
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$ V.map calculateFitness population
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in ( getFitness $ V.head selected
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, V.map getGenotype selected
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)
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shouldContinue :: [Double] -- ^ Fitness history
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-> Bool
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shouldContinue (x:y:_) = x /= y
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shouldContinue _ = True
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evolutionLoop :: Species e g
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=> e -- ^ Environment
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-> [Double] -- ^ Fitness history
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-> V.Vector g -- ^ Survivors from previous generation
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-> IO (V.Vector g) -- ^ Final population
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evolutionLoop environment history survivors =
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do
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population <- evolvePopulation environment survivors
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let (bestFitness, survivors') = selectSurvivors environment population
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history' = bestFitness : history
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printf "Generation: %3i Fitness: %7.1f\n"
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(length history') (head history')
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if shouldContinue history'
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then evolutionLoop environment history' survivors'
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else return survivors'
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-- | Run the genetic algorithm.
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evolve :: Species e g
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=> e -- ^ Environment
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-> IO g -- ^ Optimal genotype
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evolve environment = do
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population <- initialPopulation environment
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survivors <- evolutionLoop environment [] population
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return $ V.head survivors
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