ifs.dbt
Class DbtPropagation

java.lang.Object
  ifs.extension.Extension
      ifs.extension.MacPropagation
          ifs.dbt.DbtPropagation

All Implemented Interfaces:

ModelListener, SolverListener

public class DbtPropagation
extends MacPropagation
implements SolverListener

Maintenance of arc consistency in dynamic backtracking.

The difference between MacPropagation and this DBT propagation is that all not-assigned values of an assigned variable are marked as nogood. Also, when a dead end is reached, unassignment or failure takes place.

This IFS solver extension is to be used only in case of dynamic backtracking and it has no parameters.

Version:

1.0

Author:

Tomáš Müller

Field Summary

Fields inherited from class ifs.extension.MacPropagation

iConstraints, iIteration

Constructor Summary

DbtPropagation(Solver solver, DataProperties properties)
Constructor.

Method Summary

void	afterAssigned(long iteration, Value value) Propagation takes place every time a value is assigned to a variable.
void	afterUnassigned(long iteration, Value value) Undo propagation when a value is unassigned.
boolean	valueSelected(long iteration, Variable variable, Value value) If no value is selected (because of a dead end), make some unassignments.
boolean	variableSelected(long iteration, Variable variable) If no variable is selected (all variables are assinged), unassign the last assigned variable.

Methods inherited from class ifs.extension.MacPropagation

addConstraint, beforeAssigned, contains, goodValues, init, isGood, noGood, propagate, propagate, propagate, propagate, setGood, setNoGood, undoPropagate

Methods inherited from class ifs.extension.Extension

beforeUnassigned, constraintAdded, constraintRemoved, getInfo, getModel, getProperties, getSolver, isRegistered, register, unregister, useValueExtra, useVariableExtra, variableAdded, variableRemoved

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DbtPropagation

public DbtPropagation(Solver solver,
                      DataProperties properties)

Constructor. No parameter is taken from properties.

Method Detail

afterAssigned

public void afterAssigned(long iteration,
                          Value value)

Propagation takes place every time a value is assigned to a variable.

Prints a warning if the value is nogood (should not never happen),

sets all other values of the variable to nogood (explanation is the assigned value itself),

runs propagation.

Specified by:

afterAssigned in interface ModelListener

Overrides:

afterAssigned in class MacPropagation

Parameters:

iteration - current iteration

value - value to be assigned

See Also:

MacPropagation.propagate(Variable)

afterUnassigned

public void afterUnassigned(long iteration,
                            Value value)

Undo propagation when a value is unassigned.

Prints an error if the value is nogood (should not never happen),

runs propagation undo.

Specified by:

afterUnassigned in interface ModelListener

Overrides:

afterUnassigned in class MacPropagation

Parameters:

iteration - current iteration

value - value to be unassigned

See Also:

MacPropagation.undoPropagate(Variable)

variableSelected

public boolean variableSelected(long iteration,
                                Variable variable)

If no variable is selected (all variables are assinged), unassign the last assigned variable.

Do not allow to select an assigned variable.

If no variable is selected (because all variables are assigned, see DbtVariableSelection):

• find the last assigned variable and
• unassign it (explanation is a union of assignments of all other variables).

Specified by:

variableSelected in interface SolverListener

Parameters:

iteration - current iteration

variable - selected variable

See Also:

DbtVariableSelection.selectVariable(Solution)

valueSelected

public boolean valueSelected(long iteration,
                             Variable variable,
                             Value value)

If no value is selected (because of a dead end), make some unassignments.

If no value is selected (e.g., because the selected variable has all values marked as nogood, see DbtValueSelection),

• compute a union of explanations of all values,
  • if it is empty fail (inconsistency is found),
• otherwise pick the last assigned variable from the computed union of explanation and unassign it
  (explanation for that is the computed union of explanations without the last assignment).

Specified by:

valueSelected in interface SolverListener

Parameters:

iteration - current iteration

variable - selected variable

value - selected variable

See Also:

DbtVariableSelection.selectVariable(Solution)