001 package net.sf.cpsolver.ifs.constant;
002
003
004 import java.util.ArrayList;
005 import java.util.List;
006
007 import net.sf.cpsolver.ifs.model.Model;
008 import net.sf.cpsolver.ifs.model.Value;
009 import net.sf.cpsolver.ifs.model.Variable;
010
011 /**
012 * Extension of the model with constant variables.
013 *
014 * Such variables are excluded from the solver process, however, they can be
015 * included in constraints. Such model can allow us to build a solution on top
016 * of another solution (e.g., committed classes in the course timetabling).
017 *
018 * Constant variable has to implement interface {@link ConstantVariable},
019 * returning {@link ConstantVariable#isConstant()} true.
020 *
021 * @version IFS 1.2 (Iterative Forward Search)<br>
022 * Copyright (C) 2006 - 2010 Tomas Muller<br>
023 * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
024 * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
025 * <br>
026 * This library is free software; you can redistribute it and/or modify
027 * it under the terms of the GNU Lesser General Public License as
028 * published by the Free Software Foundation; either version 3 of the
029 * License, or (at your option) any later version. <br>
030 * <br>
031 * This library is distributed in the hope that it will be useful, but
032 * WITHOUT ANY WARRANTY; without even the implied warranty of
033 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
034 * Lesser General Public License for more details. <br>
035 * <br>
036 * You should have received a copy of the GNU Lesser General Public
037 * License along with this library; if not see <http://www.gnu.org/licenses/>.
038 *
039 */
040
041 public class ConstantModel<V extends Variable<V, T>, T extends Value<V, T>> extends Model<V, T> {
042 private List<V> iConstantVariables = null;
043
044 /** List of constant variables */
045 public List<V> constantVariables() {
046 return iConstantVariables;
047 }
048
049 /** True, if the model contains at least one constant variable. */
050 public boolean hasConstantVariables() {
051 return iConstantVariables != null && !iConstantVariables.isEmpty();
052 }
053
054 /** True, if the given variable is constant. */
055 public boolean isConstant(V variable) {
056 return (iConstantVariables != null && variable instanceof ConstantVariable && ((ConstantVariable) variable)
057 .isConstant());
058 }
059
060 /** Adds a variable to the model */
061 @Override
062 public void addVariable(V variable) {
063 if (variable instanceof ConstantVariable && ((ConstantVariable) variable).isConstant()) {
064 if (iConstantVariables == null)
065 iConstantVariables = new ArrayList<V>();
066 variable.setModel(this);
067 iConstantVariables.add(variable);
068 if (variable.getAssignment() != null)
069 variable.assign(0L, variable.getAssignment());
070 } else
071 super.addVariable(variable);
072 }
073
074 /** Removes a variable from the model */
075 @Override
076 public void removeVariable(V variable) {
077 if (isConstant(variable)) {
078 variable.setModel(null);
079 iConstantVariables.remove(variable);
080 } else
081 super.removeVariable(variable);
082 }
083
084 /**
085 * Called before a value is assigned to its variable. Constant variables are
086 * excluded from (re)assignment.
087 */
088 @Override
089 public void beforeAssigned(long iteration, T value) {
090 if (!isConstant(value.variable()))
091 super.beforeAssigned(iteration, value);
092 }
093
094 /**
095 * Called before a value is unassigned from its variable. Constant variables
096 * are excluded from (re)assignment.
097 */
098 @Override
099 public void beforeUnassigned(long iteration, T value) {
100 if (!isConstant(value.variable()))
101 super.beforeUnassigned(iteration, value);
102 }
103
104 /**
105 * Called after a value is assigned to its variable. Constant variables are
106 * excluded from (re)assignment.
107 */
108 @Override
109 public void afterAssigned(long iteration, T value) {
110 if (!isConstant(value.variable()))
111 super.afterAssigned(iteration, value);
112 }
113
114 /**
115 * Called after a value is unassigned from its variable. Constant variables
116 * are excluded from (re)assignment.
117 */
118 @Override
119 public void afterUnassigned(long iteration, T value) {
120 if (!isConstant(value.variable()))
121 super.afterUnassigned(iteration, value);
122 }
123 }