1/*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements.  See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License.  You may obtain a copy of the License at
8 *
9 *      http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18package org.apache.commons.math.optimization.linear;
19
20import java.io.IOException;
21import java.io.ObjectInputStream;
22import java.io.ObjectOutputStream;
23import java.io.Serializable;
24
25import org.apache.commons.math.linear.MatrixUtils;
26import org.apache.commons.math.linear.RealVector;
27import org.apache.commons.math.linear.ArrayRealVector;
28
29/**
30 * An objective function for a linear optimization problem.
31 * <p>
32 * A linear objective function has one the form:
33 * <pre>
34 * c<sub>1</sub>x<sub>1</sub> + ... c<sub>n</sub>x<sub>n</sub> + d
35 * </pre>
36 * The c<sub>i</sub> and d are the coefficients of the equation,
37 * the x<sub>i</sub> are the coordinates of the current point.
38 * </p>
39 * @version $Revision: 922713 $ $Date: 2010-03-14 02:26:13 +0100 (dim. 14 mars 2010) $
40 * @since 2.0
41 */
42public class LinearObjectiveFunction implements Serializable {
43
44    /** Serializable version identifier. */
45    private static final long serialVersionUID = -4531815507568396090L;
46
47    /** Coefficients of the constraint (c<sub>i</sub>). */
48    private final transient RealVector coefficients;
49
50    /** Constant term of the linear equation. */
51    private final double constantTerm;
52
53    /**
54     * @param coefficients The coefficients for the linear equation being optimized
55     * @param constantTerm The constant term of the linear equation
56     */
57    public LinearObjectiveFunction(double[] coefficients, double constantTerm) {
58        this(new ArrayRealVector(coefficients), constantTerm);
59    }
60
61    /**
62     * @param coefficients The coefficients for the linear equation being optimized
63     * @param constantTerm The constant term of the linear equation
64     */
65    public LinearObjectiveFunction(RealVector coefficients, double constantTerm) {
66        this.coefficients = coefficients;
67        this.constantTerm = constantTerm;
68    }
69
70    /**
71     * Get the coefficients of the linear equation being optimized.
72     * @return coefficients of the linear equation being optimized
73     */
74    public RealVector getCoefficients() {
75        return coefficients;
76    }
77
78    /**
79     * Get the constant of the linear equation being optimized.
80     * @return constant of the linear equation being optimized
81     */
82    public double getConstantTerm() {
83        return constantTerm;
84    }
85
86    /**
87     * Compute the value of the linear equation at the current point
88     * @param point point at which linear equation must be evaluated
89     * @return value of the linear equation at the current point
90     */
91    public double getValue(final double[] point) {
92        return coefficients.dotProduct(point) + constantTerm;
93    }
94
95    /**
96     * Compute the value of the linear equation at the current point
97     * @param point point at which linear equation must be evaluated
98     * @return value of the linear equation at the current point
99     */
100    public double getValue(final RealVector point) {
101        return coefficients.dotProduct(point) + constantTerm;
102    }
103
104    /** {@inheritDoc} */
105    @Override
106    public boolean equals(Object other) {
107
108      if (this == other) {
109        return true;
110      }
111
112      if (other instanceof LinearObjectiveFunction) {
113          LinearObjectiveFunction rhs = (LinearObjectiveFunction) other;
114          return (constantTerm == rhs.constantTerm) && coefficients.equals(rhs.coefficients);
115      }
116
117      return false;
118    }
119
120    /** {@inheritDoc} */
121    @Override
122    public int hashCode() {
123        return Double.valueOf(constantTerm).hashCode() ^ coefficients.hashCode();
124    }
125
126    /** Serialize the instance.
127     * @param oos stream where object should be written
128     * @throws IOException if object cannot be written to stream
129     */
130    private void writeObject(ObjectOutputStream oos)
131        throws IOException {
132        oos.defaultWriteObject();
133        MatrixUtils.serializeRealVector(coefficients, oos);
134    }
135
136    /** Deserialize the instance.
137     * @param ois stream from which the object should be read
138     * @throws ClassNotFoundException if a class in the stream cannot be found
139     * @throws IOException if object cannot be read from the stream
140     */
141    private void readObject(ObjectInputStream ois)
142      throws ClassNotFoundException, IOException {
143        ois.defaultReadObject();
144        MatrixUtils.deserializeRealVector(this, "coefficients", ois);
145    }
146
147}
148