/*
* Java Genetic Algorithm Library (@__identifier__@).
* Copyright (c) @__year__@ Franz Wilhelmstötter
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Author:
* Franz Wilhelmstötter (franz.wilhelmstoetter@gmx.at)
*/
package org.jenetics.example;
import static java.lang.Math.PI;
import static java.lang.Math.abs;
import static java.lang.Math.sin;
import static org.jenetics.engine.EvolutionResult.toBestPhenotype;
import static org.jenetics.engine.limit.bySteadyFitness;
import java.util.stream.IntStream;
import org.jenetics.EnumGene;
import org.jenetics.Optimize;
import org.jenetics.PartiallyMatchedCrossover;
import org.jenetics.Phenotype;
import org.jenetics.SwapMutator;
import org.jenetics.engine.Engine;
import org.jenetics.engine.EvolutionStatistics;
import org.jenetics.engine.codecs;
public class TravelingSalesman {
// Problem initialization:
// Calculating the adjacence matrix of the "city" distances.
private static final int STOPS = 20;
private static final double[][] ADJACENCE = matrix(STOPS);
private static double[][] matrix(int stops) {
final double radius = 10.0;
double[][] matrix = new double[stops][stops];
for (int i = 0; i < stops; ++i) {
for (int j = 0; j < stops; ++j) {
matrix[i][j] = chord(stops, abs(i - j), radius);
}
}
return matrix;
}
private static double chord(int stops, int i, double r) {
return 2.0*r*abs(sin(PI*i/stops));
}
// Calculate the path length of the current genotype.
private static double dist(final int[] path) {
// Calculate the path distance.
return IntStream.range(0, STOPS)
.mapToDouble(i ->
ADJACENCE[path[i]][path[(i + 1)%STOPS]])
.sum();
}
public static void main(String[] args) {
final Engine<EnumGene<Integer>, Double> engine = Engine
.builder(
TravelingSalesman::dist,
codecs.ofPermutation(STOPS))
.optimize(Optimize.MINIMUM)
.maximalPhenotypeAge(11)
.populationSize(500)
.alterers(
new SwapMutator<>(0.2),
new PartiallyMatchedCrossover<>(0.35))
.build();
// Create evolution statistics consumer.
final EvolutionStatistics<Double, ?>
statistics = EvolutionStatistics.ofNumber();
final Phenotype<EnumGene<Integer>, Double> best =
engine.stream()
// Truncate the evolution stream after 7 "steady"
// generations.
.limit(bySteadyFitness(15))
// The evolution will stop after maximal 100
// generations.
.limit(250)
// Update the evaluation statistics after
// each generation
.peek(statistics)
// Collect (reduce) the evolution stream to
// its best phenotype.
.collect(toBestPhenotype());
System.out.println(statistics);
System.out.println(best);
}
}