001package net.sf.cpsolver.ifs.constant;
002
003
004import java.util.ArrayList;
005import java.util.List;
006
007import net.sf.cpsolver.ifs.model.Model;
008import net.sf.cpsolver.ifs.model.Value;
009import 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 Tomáš Müller<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
041public 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}