Issue with random mutation hill climbing - random

Question

Hi I'm trying to write some simple code to use random mutation hill climbing for the travelling salesman problem. I have created a Tour class as such:-
import java.util.ArrayList;
import java.util.Collections;
public class Tour
{
private ArrayList<Integer> tour;
// Specified tour
public Tour(ArrayList<Integer> tour) { this.tour = tour; }
// Random tour
public Tour(int size)
{
// Initalize tour with size
tour = new ArrayList<Integer>(size);
// Add integers up to size into ArrayList
for (int i=0; i<size; ++i) {tour.add(i);}
// Shuffle ArrayList
Collections.shuffle(tour);
}
ArrayList<Integer> getTour() {return tour;}
void printTour()
{
for (int i=0; i<tour.size(); ++i)
{
System.out.print(tour.get(i) + ", ");
}
}
// Get the distance between all tour stops using a set of distances
double getFitness (double[][] distances)
{
double s = 0;
for (int i=0; i<tour.size()-1; ++i)
{
int a = tour.get(i);
int b = tour.get(i+1);
s += distances[a][b];
}
int start_city = tour.get(0);
int end_city = tour.get(tour.size()-1);
s += distances[end_city][start_city];
return s;
}
// Makes a small change to the tour
void smallChange()
{
// Change random index values to swap
int indexfirst = CS2004.UI(0, tour.size()-1);
int indexsecond = CS2004.UI(0, tour.size()-1);
// Checks to make sure index values are not the same
while (indexsecond == indexfirst)
{
indexsecond = CS2004.UI(0, tour.size()-1);
}
// Store city value in temp variable
int indexTemp = tour.get(indexfirst);
// Swap values
tour.set(indexfirst, tour.get(indexsecond));
tour.set(indexsecond, indexTemp);
}
}
My RMHC method looks like this:-
public static Tour RMHC(double[][] distances, int iter)
{
Tour sol = new Tour(distances.length);
double oldFitness;
double fitness = 0;
Tour oldSol=null;
for (int i=0;i<iter;i++)
{
oldSol = null;
// Make old solution equal to solution before change
oldSol = new Tour(sol.getTour());
System.out.println(oldSol.getTour());
// Calculate old fitness for comparison
oldFitness = sol.getFitness(distances);
// Change solution slightly
sol.smallChange();
// Calculate new fitness
fitness = sol.getFitness(distances);
/* Compare new fitness to old fitness
* set solution back to old solution and fitness to old fitness if
* new solution is not better */
System.out.println(oldFitness + " " + fitness);
if (fitness > oldFitness) {System.out.println(oldSol.getTour()); System.out.println(sol.getTour()); sol = null; sol = new Tour(oldSol.getTour()); fitness = oldFitness;}
// Print iteration number and new fitness
System.out.println("Iteration " + (i+1) + ", fitness: " + sol.getFitness(distances));
}
return(sol);
}
The problem I'm having is that when I call my smallChange method in the RMHC it seems to change the Tour for both the old solution and the new solution. I ran this for a few iterations on a 48 size dataset and got the following output:-
[11, 6, 13, 37, 23, 45, 34, 25, 16, 39, 5, 35, 31, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 22, 44, 7, 24, 43, 14, 41, 1, 38, 40]
155843.9387676824 159088.1701641078
[31, 6, 13, 37, 23, 45, 34, 25, 16, 39, 5, 35, 11, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 22, 44, 7, 24, 43, 14, 41, 1, 38, 40]
[31, 6, 13, 37, 23, 45, 34, 25, 16, 39, 5, 35, 11, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 22, 44, 7, 24, 43, 14, 41, 1, 38, 40]
Iteration 1, fitness: 159088.1701641078
[31, 6, 13, 37, 23, 45, 34, 25, 16, 39, 5, 35, 11, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 22, 44, 7, 24, 43, 14, 41, 1, 38, 40]
159088.1701641078 144709.1336957683
Iteration 2, fitness: 144709.1336957683
[31, 6, 13, 37, 7, 45, 34, 25, 16, 39, 5, 35, 11, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 22, 44, 23, 24, 43, 14, 41, 1, 38, 40]
144709.1336957683 143387.5110957744
Iteration 3, fitness: 143387.5110957744
[31, 6, 13, 37, 7, 45, 22, 25, 16, 39, 5, 35, 11, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 34, 44, 23, 24, 43, 14, 41, 1, 38, 40]
143387.5110957744 143565.3842060348
[31, 6, 13, 37, 7, 45, 22, 25, 16, 39, 5, 35, 14, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 34, 44, 23, 24, 43, 11, 41, 1, 38, 40]
[31, 6, 13, 37, 7, 45, 22, 25, 16, 39, 5, 35, 14, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 34, 44, 23, 24, 43, 11, 41, 1, 38, 40]