org.cpsolver.ifs.dbt

Class DbtPropagation<V extends Variable<V,T>,T extends Value<V,T>>

java.lang.Object

org.cpsolver.ifs.extension.Extension<V,T>

org.cpsolver.ifs.assignment.context.ExtensionWithContext<V,T,MacPropagation.NoGood>

org.cpsolver.ifs.extension.MacPropagation<V,T>

org.cpsolver.ifs.dbt.DbtPropagation<V,T>

Type Parameters:

V - Variable

T - Value

All Implemented Interfaces:

CanHoldContext, HasAssignmentContext<V,T,MacPropagation.NoGood>, ModelListener<V,T>, SolverListener<V,T>

public class DbtPropagation<V extends Variable<V,T>,T extends Value<V,T>>
extends MacPropagation<V,T>
implements SolverListener<V,T>

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:

IFS 1.3 (Iterative Forward Search)
Copyright (C) 2006 - 2014 Tomáš Müller
muller@unitime.org
http://muller.unitime.org

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not see http://www.gnu.org/licenses.

Author:

Tomáš Müller

Nested Class Summary

Nested classes/interfaces inherited from class org.cpsolver.ifs.extension.MacPropagation

MacPropagation.NoGood

Field Summary

Fields inherited from class org.cpsolver.ifs.extension.MacPropagation

iConstraints, iIteration

Fields inherited from interface org.cpsolver.ifs.assignment.context.CanHoldContext

sMaxSize

Constructor Summary

Constructors

Constructor and Description
DbtPropagation(Solver<V,T> solver, DataProperties properties) Constructor.

Method Summary

Modifier and Type	Method and Description
void	afterAssigned(Assignment<V,T> assignment, long iteration, T value) Propagation takes place every time a value is assigned to a variable.
void	afterUnassigned(Assignment<V,T> assignment, long iteration, T value) Undo propagation when a value is unassigned.
void	neighbourFailed(Assignment<V,T> assignment, long iteration, Neighbour<V,T> neighbour) Called when ParallelSolver failed to assign the given neighbour
boolean	neighbourSelected(Assignment<V,T> assignment, long iteration, Neighbour<V,T> neighbour) A neighbour was selected
boolean	valueSelected(Assignment<V,T> assignment, long iteration, V variable, T value) If no value is selected (because of a dead end), make some unassignments.
boolean	variableSelected(Assignment<V,T> assignment, long iteration, V variable) If no variable is selected (all variables are assinged), unassign the last assigned variable.

Methods inherited from class org.cpsolver.ifs.extension.MacPropagation

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

Methods inherited from class org.cpsolver.ifs.assignment.context.ExtensionWithContext

getAssignmentContextReference, getContext, getContext, init, setAssignmentContextReference, unregister

Methods inherited from class org.cpsolver.ifs.extension.Extension

beforeUnassigned, constraintAdded, constraintRemoved, getModel, getProperties, getSolver, isRegistered, register, 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<V,T> solver,
                      DataProperties properties)

Constructor. No parameter is taken from properties.

Parameters:

solver - current solver

properties - solver configuration

Method Detail

afterAssigned

public void afterAssigned(Assignment<V,T> assignment,
                          long iteration,
                          T 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<V extends Variable<V,T>,T extends Value<V,T>>

Overrides:

afterAssigned in class MacPropagation<V extends Variable<V,T>,T extends Value<V,T>>

Parameters:

assignment - current assignment

iteration - current iteration

value - value to be assigned

See Also:

MacPropagation.propagate(Assignment, Variable)

afterUnassigned

public void afterUnassigned(Assignment<V,T> assignment,
                            long iteration,
                            T 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<V extends Variable<V,T>,T extends Value<V,T>>

Overrides:

afterUnassigned in class MacPropagation<V extends Variable<V,T>,T extends Value<V,T>>

Parameters:

assignment - current assignment

iteration - current iteration

value - value to be unassigned

See Also:

MacPropagation.undoPropagate(Assignment, Variable)

variableSelected

public boolean variableSelected(Assignment<V,T> assignment,
                                long iteration,
                                V 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<V extends Variable<V,T>,T extends Value<V,T>>

Parameters:

assignment - current assignment

iteration - current iteration

variable - selected variable

Returns:

if false is returned the variable will be discarded (search continues with the next variable selection)

See Also:

DbtVariableSelection.selectVariable(Solution)

valueSelected

public boolean valueSelected(Assignment<V,T> assignment,
                             long iteration,
                             V variable,
                             T 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<V extends Variable<V,T>,T extends Value<V,T>>

Parameters:

assignment - current assignment

iteration - current iteration

variable - selected variable

value - selected variable

Returns:

if false is returned the selected value is not assigned

See Also:

DbtVariableSelection.selectVariable(Solution)

neighbourSelected

public boolean neighbourSelected(Assignment<V,T> assignment,
                                 long iteration,
                                 Neighbour<V,T> neighbour)

Description copied from interface: SolverListener

A neighbour was selected

Specified by:

neighbourSelected in interface SolverListener<V extends Variable<V,T>,T extends Value<V,T>>

Parameters:

assignment - current assignment

iteration - current iteration

neighbour - neighbour

Returns:

if false is returned the selected neighbour is not assigned

neighbourFailed

public void neighbourFailed(Assignment<V,T> assignment,
                            long iteration,
                            Neighbour<V,T> neighbour)

Description copied from interface: SolverListener

Called when ParallelSolver failed to assign the given neighbour

Specified by:

neighbourFailed in interface SolverListener<V extends Variable<V,T>,T extends Value<V,T>>

Parameters:

assignment - current assignment

iteration - current iteration

neighbour - neighbour