public Assignment <TVar, TVal> Optimize(OptimizationProblem <TVar, TVal> problem)
{
var currentAssignment = Solve(problem);
var nextAssignment = currentAssignment;
while (nextAssignment != null)
{
this.best = this.costFunction.Cost(currentAssignment);
nextAssignment = Solve(problem);
if (nextAssignment != null)
{
currentAssignment = nextAssignment;
}
}
return(currentAssignment);
}
public Problem(OptimizationProblem <TVar, TVal> oProblem) :
this(oProblem.Variables, oProblem.Constraints, oProblem.InitialAssignment)
{
}
private Assignment <TVar, TVal> RecursiveBacktrack(Assignment <TVar, TVal> currentAssignment, OptimizationProblem <TVar, TVal> problem, CancellationToken cancellationToken)
{
// This is based on an algorithm from
// "Artificial Intelligence: A Modern Approach" 2nd Edition by Stuart Russel and Perter Norvig (page 142).
if (currentAssignment.IsComplete(problem.Variables))
{
return(currentAssignment);
}
cancellationToken.ThrowIfCancellationRequested();
Variable <TVar, TVal> variable = VariableSelectionStrategy.SelectUnassignedVariable(problem.Variables, currentAssignment, new Problem <TVar, TVal>(problem));
IEnumerable <TVal> domain = DomainSortStrategy.GetOrderedDomain(variable, currentAssignment, new Problem <TVar, TVal>(problem));
foreach (var value in domain)
{
var nextAssignment = currentAssignment.Assign(variable, value);
if (this.costFunction.Cost(nextAssignment) >= this.best)
{
continue;
}
if (nextAssignment.IsConsistent(problem.Constraints))
{
var result = RecursiveBacktrack(nextAssignment, problem, cancellationToken);
if (result != null)
{
return(result);
}
}
}
return(null);
}
/// <summary>
/// Attempts to solve the specified constraint satisfaction problem.
/// If the problem could not be solved then this will return null.
/// </summary>
/// <param name="problem">the problem to solve</param>
/// <returns>a complete assignment or null</returns>
/// <exception cref="ArgumentNullException">if the problem is null</exception>
public Assignment <TVar, TVal> Solve(OptimizationProblem <TVar, TVal> problem)
{
return(Solve(problem, CancellationToken.None));
}
