View Javadoc

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 }