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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   * @version $Id: LinearObjectiveFunction.java 1435539 2013-01-19 13:27:24Z tn $
41   * @since 2.0
42   */
43  public class LinearObjectiveFunction
44      implements MultivariateFunction,
45                 OptimizationData,
46                 Serializable {
47      /** Serializable version identifier. */
48      private static final long serialVersionUID = -4531815507568396090L;
49      /** Coefficients of the linear equation (c<sub>i</sub>). */
50      private final transient RealVector coefficients;
51      /** Constant term of the linear equation. */
52      private final double constantTerm;
53  
54      /**
55       * @param coefficients Coefficients for the linear equation being optimized.
56       * @param constantTerm Constant term of the linear equation.
57       */
58      public LinearObjectiveFunction(double[] coefficients, double constantTerm) {
59          this(new ArrayRealVector(coefficients), constantTerm);
60      }
61  
62      /**
63       * @param coefficients Coefficients for the linear equation being optimized.
64       * @param constantTerm Constant term of the linear equation.
65       */
66      public LinearObjectiveFunction(RealVector coefficients, double constantTerm) {
67          this.coefficients = coefficients;
68          this.constantTerm = constantTerm;
69      }
70  
71      /**
72       * Gets the coefficients of the linear equation being optimized.
73       *
74       * @return coefficients of the linear equation being optimized.
75       */
76      public RealVector getCoefficients() {
77          return coefficients;
78      }
79  
80      /**
81       * Gets the constant of the linear equation being optimized.
82       *
83       * @return constant of the linear equation being optimized.
84       */
85      public double getConstantTerm() {
86          return constantTerm;
87      }
88  
89      /**
90       * Computes the value of the linear equation at the current point.
91       *
92       * @param point Point at which linear equation must be evaluated.
93       * @return the value of the linear equation at the current point.
94       */
95      public double value(final double[] point) {
96          return value(new ArrayRealVector(point, false));
97      }
98  
99      /**
100      * Computes the value of the linear equation at the current point.
101      *
102      * @param point Point at which linear equation must be evaluated.
103      * @return the value of the linear equation at the current point.
104      */
105     public double value(final RealVector point) {
106         return coefficients.dotProduct(point) + constantTerm;
107     }
108 
109     @Override
110     public boolean equals(Object other) {
111         if (this == other) {
112             return true;
113         }
114         if (other instanceof LinearObjectiveFunction) {
115             LinearObjectiveFunction rhs = (LinearObjectiveFunction) other;
116           return (constantTerm == rhs.constantTerm) && coefficients.equals(rhs.coefficients);
117         }
118 
119         return false;
120     }
121 
122     @Override
123     public int hashCode() {
124         return Double.valueOf(constantTerm).hashCode() ^ coefficients.hashCode();
125     }
126 
127     /**
128      * Serialize the instance.
129      * @param oos stream where object should be written
130      * @throws IOException if object cannot be written to stream
131      */
132     private void writeObject(ObjectOutputStream oos)
133         throws IOException {
134         oos.defaultWriteObject();
135         MatrixUtils.serializeRealVector(coefficients, oos);
136     }
137 
138     /**
139      * Deserialize the instance.
140      * @param ois stream from which the object should be read
141      * @throws ClassNotFoundException if a class in the stream cannot be found
142      * @throws IOException if object cannot be read from the stream
143      */
144     private void readObject(ObjectInputStream ois)
145       throws ClassNotFoundException, IOException {
146         ois.defaultReadObject();
147         MatrixUtils.deserializeRealVector(this, "coefficients", ois);
148     }
149 }