106 lines
3.0 KiB
Java
106 lines
3.0 KiB
Java
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import javax.swing.*;
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import java.awt.*;
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import java.util.Random;
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public class SimulatedAnnealing extends JFrame {
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Random rnd = new Random(1);
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int n = rnd.nextInt(300) + 250;
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int[] bestState;
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double[] x = new double[n];
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double[] y = new double[n];
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{
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for (int i = 0; i < n; i++) {
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x[i] = rnd.nextDouble();
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y[i] = rnd.nextDouble();
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}
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}
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public void anneal() {
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int[] curState = new int[n];
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for (int i = 0; i < n; i++)
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curState[i] = i;
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double curEnergy = eval(curState);
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bestState = curState.clone();
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double bestEnergy = curEnergy;
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for (double temperature = 0.1, coolingFactor = 0.999999; temperature > 1e-4; temperature *= coolingFactor) {
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int i = rnd.nextInt(n);
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int j = (i + 1 + rnd.nextInt(n - 2)) % n;
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int i1 = (i - 1 + n) % n;
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int j1 = (j + 1) % n;
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double delta = dist(x[curState[i1]], y[curState[i1]], x[curState[j]], y[curState[j]])
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+ dist(x[curState[i]], y[curState[i]], x[curState[j1]], y[curState[j1]])
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- dist(x[curState[i1]], y[curState[i1]], x[curState[i]], y[curState[i]])
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- dist(x[curState[j]], y[curState[j]], x[curState[j1]], y[curState[j1]]);
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if (delta < 0 || Math.exp(-delta / temperature) > rnd.nextDouble()) {
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reverse(curState, i, j);
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curEnergy += delta;
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if (bestEnergy > curEnergy) {
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bestEnergy = curEnergy;
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System.arraycopy(curState, 0, bestState, 0, n);
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repaint();
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}
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}
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}
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}
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// http://en.wikipedia.org/wiki/2-opt
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static void reverse(int[] p, int i, int j) {
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int n = p.length;
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// reverse order from i to j
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while (i != j) {
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int t = p[j];
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p[j] = p[i];
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p[i] = t;
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i = (i + 1) % n;
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if (i == j) break;
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j = (j - 1 + n) % n;
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}
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}
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double eval(int[] state) {
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double res = 0;
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for (int i = 0, j = state.length - 1; i < state.length; j = i++)
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res += dist(x[state[i]], y[state[i]], x[state[j]], y[state[j]]);
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return res;
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}
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static double dist(double x1, double y1, double x2, double y2) {
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double dx = x1 - x2;
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double dy = y1 - y2;
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return Math.sqrt(dx * dx + dy * dy);
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}
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// visualization code
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public SimulatedAnnealing() {
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setContentPane(new JPanel() {
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protected void paintComponent(Graphics g) {
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super.paintComponent(g);
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((Graphics2D) g).setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
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((Graphics2D) g).setStroke(new BasicStroke(3));
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g.setColor(Color.BLUE);
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int w = getWidth() - 5;
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int h = getHeight() - 30;
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for (int i = 0, j = n - 1; i < n; j = i++)
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g.drawLine((int) (x[bestState[i]] * w), (int) ((1 - y[bestState[i]]) * h),
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(int) (x[bestState[j]] * w), (int) ((1 - y[bestState[j]]) * h));
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g.setColor(Color.RED);
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for (int i = 0; i < n; i++)
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g.drawOval((int) (x[i] * w) - 1, (int) ((1 - y[i]) * h) - 1, 3, 3);
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g.setColor(Color.BLACK);
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g.drawString(String.format("length: %.3f", eval(bestState)), 5, h + 20);
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}
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});
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setSize(new Dimension(600, 600));
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setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
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setVisible(true);
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new Thread(this::anneal).start();
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}
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public static void main(String[] args) {
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new SimulatedAnnealing();
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}
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}
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