public IEnumerable <T> Expand(ISearchProblem <A, S, C> problem, T node)
{
var successors = problem.Successors(node.State);
// Debug
#if VERBOSE_DEBUG
Console.WriteLine(String.Format("There are {0} successors for {1}", successors.Count(), node));
Console.WriteLine(String.Format("This node has a current path cost of {0}", node.PathCost));
#endif
foreach (var successor in successors)
{
var action = successor.Item1;
var state = successor.Item2;
var next = CreateNode(node, state);
next.Action = action;
next.StepCost = problem.StepCost(node.State, action, state);
next.Heuristic = problem.Heuristic(state);
#if VERBOSE_DEBUG
System.Diagnostics.Trace.WriteLine(" Action = " + next.Action + ", g(n') = " + next.PathCost + ", h(n') = " + next.Heuristic);
#endif
yield return(next);
}
}
private C RBFS(T node, C F_N, C bound)
{
var f_N = problem.Heuristic(node.State);
if (f_N.CompareTo(bound) > 0)
{
return(f_N);
}
if (problem.IsGoal(node.State))
{
throw new Exception();
}
var children = Expander.Expand(problem, node);
if (!children.Any())
{
return(Cost.Maximum());
}
foreach (var N_i in children)
{
if (f_N.CompareTo(F_N) < 0)
{
N_i.F = F_N.Max(N_i.EstCost);
}
else
{
N_i.F = N_i.EstCost;
}
}
children = children.OrderBy(x => x.F);
/*
* RBFS (node: N, value: F(N), bound: B)
* IF f(N)>B, RETURN f(N)
* IF N is a goal, EXIT algorithm
* IF N has no children, RETURN infinity
* FOR each child Ni of N,
* IF f(N)<F(N), F[i] := MAX(F(N),f(Ni))
* ELSE F[i] := f(Ni)
* sort Ni and F[i] in increasing order of F[i]
* IF only one child, F[2] := infinity
* WHILE (F[1] <= B and F[1] < infinity)
* F[1] := RBFS(N1, F[1], MIN(B, F[2]))
* insert Ni and F[1] in sorted order
* RETURN F[1]
*/
}