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 package org.apache.commons.math3.optim.linear;
18
19 import java.io.IOException;
20 import java.io.ObjectInputStream;
21 import java.io.ObjectOutputStream;
22 import java.io.Serializable;
23 import org.apache.commons.math3.analysis.MultivariateFunction;
24 import org.apache.commons.math3.linear.MatrixUtils;
25 import org.apache.commons.math3.linear.RealVector;
26 import org.apache.commons.math3.linear.ArrayRealVector;
27 import org.apache.commons.math3.optim.OptimizationData;
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 *
40 * @since 2.0
41 */
42 public class LinearObjectiveFunction
43 implements MultivariateFunction,
44 OptimizationData,
45 Serializable {
46 /** Serializable version identifier. */
47 private static final long serialVersionUID = -4531815507568396090L;
48 /** Coefficients of the linear equation (c<sub>i</sub>). */
49 private final transient RealVector coefficients;
50 /** Constant term of the linear equation. */
51 private final double constantTerm;
52
53 /**
54 * @param coefficients Coefficients for the linear equation being optimized.
55 * @param constantTerm 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 Coefficients for the linear equation being optimized.
63 * @param constantTerm 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 * Gets the coefficients of the linear equation being optimized.
72 *
73 * @return coefficients of the linear equation being optimized.
74 */
75 public RealVector getCoefficients() {
76 return coefficients;
77 }
78
79 /**
80 * Gets the constant of the linear equation being optimized.
81 *
82 * @return constant of the linear equation being optimized.
83 */
84 public double getConstantTerm() {
85 return constantTerm;
86 }
87
88 /**
89 * Computes the value of the linear equation at the current point.
90 *
91 * @param point Point at which linear equation must be evaluated.
92 * @return the value of the linear equation at the current point.
93 */
94 public double value(final double[] point) {
95 return value(new ArrayRealVector(point, false));
96 }
97
98 /**
99 * Computes the value of the linear equation at the current point.
100 *
101 * @param point Point at which linear equation must be evaluated.
102 * @return the value of the linear equation at the current point.
103 */
104 public double value(final RealVector point) {
105 return coefficients.dotProduct(point) + constantTerm;
106 }
107
108 @Override
109 public boolean equals(Object other) {
110 if (this == other) {
111 return true;
112 }
113 if (other instanceof LinearObjectiveFunction) {
114 LinearObjectiveFunction rhs = (LinearObjectiveFunction) other;
115 return (constantTerm == rhs.constantTerm) && coefficients.equals(rhs.coefficients);
116 }
117
118 return false;
119 }
120
121 @Override
122 public int hashCode() {
123 return Double.valueOf(constantTerm).hashCode() ^ coefficients.hashCode();
124 }
125
126 /**
127 * Serialize the instance.
128 * @param oos stream where object should be written
129 * @throws IOException if object cannot be written to stream
130 */
131 private void writeObject(ObjectOutputStream oos)
132 throws IOException {
133 oos.defaultWriteObject();
134 MatrixUtils.serializeRealVector(coefficients, oos);
135 }
136
137 /**
138 * Deserialize the instance.
139 * @param ois stream from which the object should be read
140 * @throws ClassNotFoundException if a class in the stream cannot be found
141 * @throws IOException if object cannot be read from the stream
142 */
143 private void readObject(ObjectInputStream ois)
144 throws ClassNotFoundException, IOException {
145 ois.defaultReadObject();
146 MatrixUtils.deserializeRealVector(this, "coefficients", ois);
147 }
148 }