base fitness function for NEAT

createFitnessFunction.js

const createFitnessFunction = (dataset, { repeat = 1, cost }) => {
  return network => {
    let score = 0
    for (let i = 0; i < repeat; i++) {
      const result = network.test(dataset, cost)

      if (!result || typeof result.error === 'undefined') {
        throw new Error('The test method did not return a valid result with an error property.')
      }

      score -= result.error
    }

    score -= network.topologySize * growthPenalty
    score = isNaN(score) ? -Infinity : score

    return score / repeat
  }
}