calculateFitness.js

function calculateFitness(network, data) {
  let fitness = 0;
  for (const { input, output } of data) {
    const prediction = network.propagate(input);
    const error = output[0] - prediction[0];
    fitness += 1 - Math.abs(error * error);
  }
  // Normalize the fitness value by dividing it by the number of data points
  return fitness / data.length;
}