public static BB_Node create_BB_node(Tuple <int, int> varToFix, bool fix1, BB_Node parent, double UB)
{
statistics.n_BB_nodes += 1;
BB_Node no = new BB_Node(varToFix, fix1, parent, UB);
return(no);
}
public static double update_UB(BB_Node node)
{
if (node.left_child == null || node.right_child == null)
{
return(node.UB);
}
return(node.UB = Math.Min(update_UB(node.left_child), update_UB(node.right_child)));
}
public BB_Node(Tuple <int, int> varToFix, bool fix1, BB_Node parent, double UB)
{
this.varToFix = varToFix;
this.fix1 = fix1;
this.parent = parent;
this.left_child = null;
this.right_child = null;
this.UB = UB;
}
public static void add_branch_contraints(BB_Node n_i)
{
if (n_i.parent != null)
{
if (n_i.fix1)
{
X[n_i.varToFix.Item1, n_i.varToFix.Item2].LB = 1;
}
else
{
X[n_i.varToFix.Item1, n_i.varToFix.Item2].UB = 0;
}
add_branch_contraints(n_i.parent);
}
}
public static BB_Node select_BB_node(List <BB_Node> L)
{
BB_Node selected_node = null;
double max_UB = 0.0;
foreach (BB_Node node in L)
{
if (node.UB > max_UB)
{
max_UB = node.UB;
selected_node = node;
}
}
L.Remove(selected_node);
return(selected_node);
}
public static void BranchAndBound()
{
var stopwatch = new Stopwatch();
stopwatch.Start();
build_initial_model(true);
int[,] best_sol = statistics.solucao_heuristica;
double z_ = statistics.heuristic_sol_val;
BB_Node n_0 = create_BB_node(new Tuple <int, int>(-1, -1), false, null, int.MaxValue);
List <BB_Node> L = new List <BB_Node>();
add_BB_node(L, n_0);
var is_root_node = true;
BB_Node root_node = null;
while (L.Count != 0)
{
if (is_root_node == false)
{
update_UB(root_node);
if (root_node.UB >= z_ + e)
{
break;
}
}
stopwatch.Stop();
statistics.spent_time_in_seconds = stopwatch.ElapsedMilliseconds;
if (statistics.spent_time_in_seconds / 1000 > config.time_limit)
{
time_limit_exceeded(best_sol, z_, root_node.UB);
return;
}
stopwatch.Start();
BB_Node n_i = select_BB_node(L);
clear_branch_contraints();
add_branch_contraints(n_i);
var status = solve_LP();
double z_i;
if (status == 3)
{
continue;
}
else
{
z_i = model.ObjVal;
n_i.UB = z_i;
if (is_root_node)
{
statistics.first_linear_relax_val = z_i;
root_node = n_i;
is_root_node = false;
}
}
if (z_i >= z_ + e)
{
continue;
}
if (is_integer())
{
z_ = z_i;
copy_solution(best_sol);
continue;
}
Tuple <int, int> i_var = select_frac_var();
n_i.left_child = create_BB_node(i_var, true, n_i, z_i);
n_i.right_child = create_BB_node(i_var, false, n_i, z_i);
add_BB_node(L, n_i.left_child);
add_BB_node(L, n_i.right_child);
}
stopwatch.Stop();
statistics.spent_time_in_seconds = stopwatch.Elapsed.TotalSeconds;
statistics.objective_value = z_;
print_solution(best_sol);
}
public static void add_BB_node(List <BB_Node> L, BB_Node no)
{
L.Add(no);
}
