net.sf.cpsolver.exam.heuristics
Class ExamTabuSearch

java.lang.Object
  extended by net.sf.cpsolver.exam.heuristics.ExamTabuSearch
All Implemented Interfaces:
NeighbourSelection<Exam,ExamPlacement>, ValueSelection<Exam,ExamPlacement>

public class ExamTabuSearch
extends Object
implements NeighbourSelection<Exam,ExamPlacement>, ValueSelection<Exam,ExamPlacement>

Tabu search algorithm.

If used as NeighbourSelection, the most improving (re)assignment of a value to a variable is returned (all variables and all their values are enumerated). If there are more than one of such assignments, one is selected randomly. A returned assignment can cause unassignment of other existing assignments. The search is stopped ( selectNeighbour(Solution) returns null) after TabuSearch.MaxIdle idle (not improving) iterations.

If used as ValueSelection, the most improving (re)assignment of a value to a given variable is returned (all values of the given variable are enumerated). If there are more than one of such assignments, one is selected randomly. A returned assignment can cause unassignment of other existing assignments.

To avoid cycling, a tabu is maintainded during the search. It is the list of the last n selected values. A selection of a value that is present in the tabu list is only allowed when it improves the best ever found solution.

The minimum size of the tabu list is TabuSearch.MinSize, maximum size is TabuSearch.MaxSize (tabu list is not used when both sizes are zero). The current size of the tabu list starts at MinSize (and is reset to MinSize every time a new best solution is found), it is increased by one up to the MaxSize after TabuSearch.MaxIdle / (MaxSize - MinSize) non-improving iterations.

Conflict-based Statistics ConflictStatistics (CBS) can be used instead of (or together with) tabu list, when CBS is used as a solver extension.

Version:
ExamTT 1.2 (Examination Timetabling)
Copyright (C) 2008 - 2010 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/.

Constructor Summary
ExamTabuSearch(DataProperties properties)
           TabuSearch.MaxIdle ... maximum number of idle iterations (default is 10000) TabuSearch.MinSize ... minimum size of the tabu list TabuSearch.MaxSize ... maximum size of the tabu list Value.ValueWeight ... weight of a value (i.e., Value.toDouble()) Value.ConflictWeight ... weight of a conflicting value (see Model.conflictValues(Value)), it is also weighted by the past occurrences when conflict-based statistics is used
 
Method Summary
 void init(Solver<Exam,ExamPlacement> solver)
          Initialization
 Neighbour<Exam,ExamPlacement> selectNeighbour(Solution<Exam,ExamPlacement> solution)
          Neighbor selection
 ExamPlacement selectValue(Solution<Exam,ExamPlacement> solution, Exam exam)
          Value selection
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

ExamTabuSearch

public ExamTabuSearch(DataProperties properties)
               throws Exception

Throws:
Exception
Method Detail

init

public void init(Solver<Exam,ExamPlacement> solver)
Initialization

Specified by:
init in interface NeighbourSelection<Exam,ExamPlacement>
Specified by:
init in interface ValueSelection<Exam,ExamPlacement>

selectNeighbour

public Neighbour<Exam,ExamPlacement> selectNeighbour(Solution<Exam,ExamPlacement> solution)
Neighbor selection

Specified by:
selectNeighbour in interface NeighbourSelection<Exam,ExamPlacement>
Parameters:
solution - given solution
Returns:
a neighbour assignment

selectValue

public ExamPlacement selectValue(Solution<Exam,ExamPlacement> solution,
                                 Exam exam)
Value selection

Specified by:
selectValue in interface ValueSelection<Exam,ExamPlacement>
Parameters:
solution - current solution
exam - selected variable