public bool CheckConstraint(Solution candidate)
{
// check routes
for (int i = 0; i < car_number; i++)
{
int route_cost = EvaluateRouteCost(candidate.GetRoute(i)); //eval each route cost
if (route_cost > constraint)
{
return false; // reject candidate
}
}
return true;
}
// clone
public Solution CloneSolution()
{
Solution s = new Solution(this.car_number);
s.cost = 0;
// initialize array of linked lists
for (int i = 0; i < car_number; i++)
{
//get city in each route
foreach (int city in this.GetRoute(i))
{
s.GetRoute(i).AddLast(city);
}
}
return s;
}
//---------------------------------------------------------------------------------------
// FITNESS FUNCTION
// fitness function = for each car route
// (sum of all city distances + distance from depot to first city
// + distance from last city back to depot)
// + sum of all service times in each city
public int EvaluateCost(Solution soln)
{
// go through array of routes
for (int x = 0; x < soln.GetLength(); x++)
{
LinkedList<int> route = soln.GetRoute(x);
if (route.Count > 0)
{
// distance from depot to first city
int city = Convert.ToInt16(route.First.Value);
soln.AddCost(depot[city]); //distance from depot to first
city = Convert.ToInt16(route.Last.Value);
soln.AddCost(depot[city]); //distance from depot to last
// go through route's cities and add distances
for (int a = 1; a < route.Count; a++)
{
//start with city -1 and city and add distances
soln.AddCost(distance[route.ElementAt(a - 1), route.ElementAt(a)]);
//add service times for each city
soln.AddCost(service[route.ElementAt(a - 1)]);
}
}
}
return soln.GetCost();
}
//---------------------------------------------------------------------------------------
// OPERATOR
// 1. switch city from 1 route to another
// 2. switch order of city in route
public Solution SwitchCityRoute(Solution soln)
{
// first random route
int random_route1 = r.Next(car_number - 1);
// make sure route is not empty
while (soln.GetRoute(random_route1).Count < 1)
{
random_route1 = r.Next(car_number - 1);
}
// second random route
int random_route2 = r.Next(car_number - 1);
// make sure route2 is not same as route1
while (random_route1 == random_route2)
{
random_route2 = r.Next(car_number - 1);
}
// route1 and route2 are non-empty, so can trade cities
if (soln.GetRoute(random_route2).Count > 1)
{
int random_city1 = r.Next(soln.GetRoute(random_route1).Count - 1); //random city position from route1
int random_city2 = r.Next(soln.GetRoute(random_route2).Count - 1); //random city position from route2
int city1 = soln.GetRoute(random_route1).ElementAt(random_city1); // city 1
int city2 = soln.GetRoute(random_route2).ElementAt(random_city2); //city 2
// remove city 1 from route 1 and add it to route 2
soln.GetRoute(random_route1).Remove(city1);
soln.GetRoute(random_route2).AddLast(city1);
// remove city 2 from route 2 and add it to route 1
soln.GetRoute(random_route2).Remove(city2);
soln.GetRoute(random_route1).AddLast(city2);
}
else if (soln.GetRoute(random_route2).Count == 1) //one city in route 2
{
int random_city1 = r.Next(soln.GetRoute(random_route1).Count - 1); //random city position from route1
int random_city2 = 0; // first city position from route2
int city1 = soln.GetRoute(random_route1).ElementAt(random_city1); // city 1
int city2 = soln.GetRoute(random_route2).ElementAt(random_city2); //city 2
// remove city 1 from route 1 and add it to route 2
soln.GetRoute(random_route1).Remove(city1);
soln.GetRoute(random_route2).AddLast(city1);
// remove city 2 from route 2 and add it to route 1
soln.GetRoute(random_route2).Remove(city2);
soln.GetRoute(random_route1).AddLast(city2);
}
else // route2 is empty
{
// remove city1 from route 1 and add it to route2
int random_city1 = r.Next(soln.GetRoute(random_route1).Count - 1); //random city position from route1
int city1 = soln.GetRoute(random_route1).ElementAt(random_city1); // city 1
soln.GetRoute(random_route1).Remove(city1); //remove from route1
soln.GetRoute(random_route2).AddLast(city1); //add to route2
}
return soln;
}
public void SwitchCityOrder(Solution soln)
{
// first random route
int random_route1 = r.Next(car_number - 1);
// make sure has more than 1 city in it
while (soln.GetRoute(random_route1).Count < 2)
{
random_route1 = r.Next(car_number - 1);
}
int city1 = soln.GetRoute(random_route1).ElementAt(0); // remove first city
soln.GetRoute(random_route1).RemoveFirst(); // remove first city
soln.GetRoute(random_route1).AddLast(city1); // add it to the end
}
public bool SolutionAcceptanceConstraint(Solution best, Solution candidate)
{
if (CheckConstraint(candidate) == false)
{
return false; // reject candidate solution
}
if (best.GetCost() - candidate.GetCost() > 0) // candidate cost is less
{
return true; // candidate is accepted
}
else
{
// accpetance probability = e^-cost/temp
int negcost = candidate.GetCost() - (2 * candidate.GetCost());
double exp = (double)negcost / (double)temperature;
double prob = Math.Exp(exp); // acceptance probability
double threshold = r.NextDouble(); // acceptance threshold - random
if (prob.CompareTo(threshold) > 0) // if accept prob > accept thresh
{
//Console.WriteLine("probability of acceptance: {0}\nthreshold of acceptance: {1}",
// prob, threshold);
return true; // candidate accepted
}
}
return false; // candidate not accepted
}
public void RunPartAWithoutConstraint()
{
Solution best_soln = new Solution(car_number);
// random initial solution
//go through all cities
//add them randomly to a car
for (int i = 0; i < cities; i++)
{
int random = r.Next(car_number - 1);
best_soln.GetRoute(random).AddLast(i);
}
int best_cost = EvaluateCost(best_soln); //eval initial cost
Console.WriteLine("INITIAL SOLUTION");
best_soln.PrintSolution();
// start SA processs
while (temperature != 0)
{
int count = iterations;
// # of iterations per temperature
while (count > 0)
{
// create new solution
Solution candidate = best_soln.CloneSolution();
// operator selection - switch cities between routes
// switch city order within a route
int operation = r.Next(1, 3);
if (operation % 2 == 0)
{
// swtich cities between routes
candidate = SwitchCityRoute(candidate);
}
else
{
// switch city order
SwitchCityOrder(candidate);
}
int current_cost = EvaluateCost(candidate);
//candidate.PrintSolution();
// figure out if solution is going to be the best
if (SolutionAcceptance(best_soln, candidate) == true)
{
best_soln = candidate; // candidate is new best
best_cost = candidate.GetCost();
}
Console.WriteLine("Temperature: {0}, Count: {1}", temperature, count);
best_soln.PrintSolution();
// should we store 'all time best'?
count--;
}
// decrease temperature
CoolingSchedule();
}
// print final best
Console.WriteLine("Best Solution");
best_soln.PrintSolution();
return;
}