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
18 package org.apache.commons.math.optimization.linear;
19
20 import java.io.IOException;
21 import java.io.ObjectInputStream;
22 import java.io.ObjectOutputStream;
23 import java.io.Serializable;
24
25 import org.apache.commons.math.linear.MatrixUtils;
26 import org.apache.commons.math.linear.RealVector;
27 import 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: 783702 $ $Date: 2009-06-11 04:54:02 -0400 (Thu, 11 Jun 2009) $
40 * @since 2.0
41 */
42 public 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 == null) {
113 return false;
114 }
115
116 try {
117
118 LinearObjectiveFunction rhs = (LinearObjectiveFunction) other;
119 return (constantTerm == rhs.constantTerm) && coefficients.equals(rhs.coefficients);
120
121 } catch (ClassCastException ex) {
122 // ignore exception
123 return false;
124 }
125
126 }
127
128 /** {@inheritDoc} */
129 @Override
130 public int hashCode() {
131 return Double.valueOf(constantTerm).hashCode() ^ coefficients.hashCode();
132 }
133
134 /** Serialize the instance.
135 * @param oos stream where object should be written
136 * @throws IOException if object cannot be written to stream
137 */
138 private void writeObject(ObjectOutputStream oos)
139 throws IOException {
140 oos.defaultWriteObject();
141 MatrixUtils.serializeRealVector(coefficients, oos);
142 }
143
144 /** Deserialize the instance.
145 * @param ois stream from which the object should be read
146 * @throws ClassNotFoundException if a class in the stream cannot be found
147 * @throws IOException if object cannot be read from the stream
148 */
149 private void readObject(ObjectInputStream ois)
150 throws ClassNotFoundException, IOException {
151 ois.defaultReadObject();
152 MatrixUtils.deserializeRealVector(this, "coefficients", ois);
153 }
154
155 }