/// <summary>
/// Backtrack through a variable's value sets until one is found that is arc consistent.
/// </summary>
/// <param name="currentVariableIndex">Current variable index.</param>
/// <param name="snapshotAssignment">Current snapshot of value sets.</param>
/// <param name="constraintNetwork">Constraint network.</param>
/// <returns>True if a value is found to be consistent, False if a value is not found.</returns>
private bool Backtrack(int currentVariableIndex, SnapshotLabelAssignment snapshotAssignment, ConstraintNetwork constraintNetwork)
{
// Label assignment has been successful...
if (snapshotAssignment.IsComplete() && AllVariablesTested(currentVariableIndex))
{
return(true);
}
// The unassigned variable may be a regular variable or an encapsulated variable
var currentVariable = SelectUnassignedVariable(currentVariableIndex, constraintNetwork, snapshotAssignment);
foreach (var value in OrderDomainValues(currentVariable, snapshotAssignment, constraintNetwork))
{
if (IsConsistent(value, snapshotAssignment))
{
snapshotAssignment.AssignTo(value);
// Is this the final variable?
if (AllVariablesTested(currentVariableIndex))
{
return(true);
}
if (Backtrack(currentVariableIndex + 1, snapshotAssignment, constraintNetwork))
{
return(true);
}
}
snapshotAssignment.Remove(value);
}
return(false);
}
/// <summary>
/// Is the value set arc consistent.
/// </summary>
/// <param name="valueSet">Value set.</param>
/// <param name="assignment">Current variable label assignments.</param>
/// <returns>True if arc consistent, False if not arc consistent.</returns>
private bool IsConsistent(ValueSet valueSet, SnapshotLabelAssignment assignment)
{
/*
* All variables in the set must be consistent, either not having been assigned
* a value or having a value that is consistent with the currently assigned value.
*/
return(valueSet.Values.All(value => IsConsistent(value, assignment)));
}
private IEnumerable <BucketLabelModel> ExtractBucketLabelsFrom(SnapshotLabelAssignment assignment, ConstraintNetwork constraintNetwork)
{
var bucketLabelAccumulator = new List <BucketLabelModel>();
foreach (var bucketVariableMap in _modelSolverMap.GetBucketVariables())
{
bucketLabelAccumulator.Add(ExtractBucketLabelFrom(assignment, bucketVariableMap));
}
return(bucketLabelAccumulator);
}
/// <summary>
/// Extract a snapshot from the constraint network.
/// </summary>
/// <param name="constraintNetwork">Constraint network.</param>
/// <param name="solutionSnapshot">Solution snapshot.</param>
/// <returns>True if a snapshot was extracted, False if the snapshot could not be extracted.</returns>
internal bool ExtractFrom(ConstraintNetwork constraintNetwork, out SolutionSnapshot solutionSnapshot)
{
_constraintNetwork = constraintNetwork;
var solverVariables = constraintNetwork.GetSolverVariables();
var assignment = new SnapshotLabelAssignment(solverVariables);
_variables = new List <VariableBase>(constraintNetwork.GetVariables());
var status = Backtrack(0, assignment, constraintNetwork);
solutionSnapshot = status ? ConvertSnapshotFrom(assignment, constraintNetwork) : SolutionSnapshot.Empty;
return(status);
}
/// <summary>
/// Get all value sets for the variable.
/// </summary>
/// <param name="variable">Variable</param>
/// <param name="assignment">All value assignments.</param>
/// <param name="constraintNetwork">Constraint network.</param>
/// <returns>All value sets for the variable.</returns>
private IEnumerable <ValueSet> OrderDomainValues(VariableBase variable, SnapshotLabelAssignment assignment, ConstraintNetwork constraintNetwork)
{
switch (variable)
{
case SolverVariable solverVariable:
return(solverVariable.GetCandidates());
case EncapsulatedVariable encapsulatedVariable:
return(encapsulatedVariable.GetCandidates());
default:
throw new NotImplementedException();
}
}
private IEnumerable <SingletonVariableLabelModel> ExtractSingletonLabelsFrom(SnapshotLabelAssignment assignment, ConstraintNetwork constraintNetwork)
{
var labelAccumulator = new List <SingletonVariableLabelModel>();
foreach (var variable in constraintNetwork.GetSingletonVariables())
{
var solverVariable = _modelSolverMap.GetSolverSingletonVariableByName(variable.Name);
var labelAssignment = assignment.GetAssignmentFor(solverVariable);
var variableSolverValue = labelAssignment.Value;
var variableModel = _modelSolverMap.GetModelSingletonVariableByName(variable.Name);
var variableModelValue = ConvertSolverValueToModel(variableModel, variableSolverValue);
var label = new SingletonVariableLabelModel(variableModel, new ValueModel(variableModelValue));
labelAccumulator.Add(label);
}
return(labelAccumulator);
}
/// <summary>
/// Is the value arc consistent.
/// </summary>
/// <param name="value">Value.</param>
/// <param name="assignment">Current variable label assignments.</param>
/// <returns>True if arc consistent, False if not arc consistent.</returns>
private bool IsConsistent(Value value, SnapshotLabelAssignment assignment)
{
var variable = value.Variable;
// Has the variable been assigned a value? If it has not, then the value must be consistent
if (!assignment.IsAssigned(variable))
{
return(true);
}
var labelAssignment = assignment.GetAssignmentFor(variable);
/*
* The variable has been assigned a value, it is consistent if the
* value is the same as the assigned value.
*/
return(labelAssignment.Value == value.Content);
}
private BucketLabelModel ExtractBucketLabelFrom(SnapshotLabelAssignment assignment, OrangeBucketVariableMap bucketVariableMap)
{
var bundleLabels = new List <BundleLabelModel>();
foreach (var bundleMap in bucketVariableMap.GetBundleMaps())
{
var variableLabels = new List <SingletonVariableLabelModel>();
foreach (var variableMap in bundleMap.GetVariableMaps())
{
var solverVariable = variableMap.SolverVariable;
var labelAssignment = assignment.GetAssignmentFor(solverVariable);
var variableSolverValue = labelAssignment.Value;
var variableModel = variableMap.ModelVariable;
var variableModelValue = ConvertSolverValueToModel(bucketVariableMap.Bucket, variableSolverValue);
var label = new SingletonVariableLabelModel(variableModel, new ValueModel(variableModelValue));
variableLabels.Add(label);
}
bundleLabels.Add(new BundleLabelModel(bucketVariableMap.Bucket.Bundle, variableLabels));
}
return(new BucketLabelModel(bucketVariableMap.Bucket, bundleLabels));
}
private IEnumerable <AggregateVariableLabelModel> ExtractAggregateLabelsFrom(SnapshotLabelAssignment assignment, ConstraintNetwork constraintNetwork)
{
var aggregatorLabelAccumulator = new List <AggregateVariableLabelModel>();
foreach (var aggregateSolverVariable in constraintNetwork.GetAggregateVariables())
{
var internalAccumulator = new List <ValueModel>();
var aggregateVariableModel = _modelSolverMap.GetModelAggregateVariableByName(aggregateSolverVariable.Name);
foreach (var variable in aggregateSolverVariable.Variables)
{
var solverVariable = _modelSolverMap.GetSolverVariableByName(variable.Name);
var labelAssignment = assignment.GetAssignmentFor(solverVariable);
var variableSolverValue = labelAssignment.Value;
var variableModel = _modelSolverMap.GetInternalModelAggregateVariableByName(variable.Name);
var variableModelValue = ConvertSolverValueToModel((SingletonVariableModel)variableModel, variableSolverValue);
internalAccumulator.Add(new ValueModel(variableModelValue));
}
var label = new AggregateVariableLabelModel(aggregateVariableModel, internalAccumulator);
aggregatorLabelAccumulator.Add(label);
}
return(aggregatorLabelAccumulator);
}
private SolutionSnapshot ConvertSnapshotFrom(SnapshotLabelAssignment assignment, ConstraintNetwork constraintNetwork)
{
return(new SolutionSnapshot(ExtractSingletonLabelsFrom(assignment, constraintNetwork),
ExtractAggregateLabelsFrom(assignment, constraintNetwork),
ExtractBucketLabelsFrom(assignment, constraintNetwork)));
}
private VariableBase SelectUnassignedVariable(int currentVariableIndex, ConstraintNetwork constraintNetwork, SnapshotLabelAssignment assignment)
{
Debug.Assert(currentVariableIndex < _variables.Count, "Backtracking must never attempt to go over the end of the variables.");
return(_variables[currentVariableIndex]);
}
