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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   * @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 }