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 * https://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 /*
19 * This is not the original file distributed by the Apache Software Foundation
20 * It has been modified by the Hipparchus project
21 */
22 package org.hipparchus.optim.nonlinear.scalar;
23
24 import java.util.ArrayList;
25 import java.util.Collections;
26 import java.util.Comparator;
27 import java.util.List;
28
29 import org.hipparchus.exception.MathIllegalArgumentException;
30 import org.hipparchus.exception.NullArgumentException;
31 import org.hipparchus.optim.BaseMultiStartMultivariateOptimizer;
32 import org.hipparchus.optim.PointValuePair;
33 import org.hipparchus.random.RandomVectorGenerator;
34
35 /**
36 * Multi-start optimizer.
37 *
38 * This class wraps an optimizer in order to use it several times in
39 * turn with different starting points (trying to avoid being trapped
40 * in a local extremum when looking for a global one).
41 *
42 */
43 public class MultiStartMultivariateOptimizer
44 extends BaseMultiStartMultivariateOptimizer<PointValuePair> {
45 /** Underlying optimizer. */
46 private final MultivariateOptimizer optimizer;
47 /** Found optima. */
48 private final List<PointValuePair> optima;
49
50 /**
51 * Create a multi-start optimizer from a single-start optimizer.
52 *
53 * @param optimizer Single-start optimizer to wrap.
54 * @param starts Number of starts to perform.
55 * If {@code starts == 1}, the result will be same as if {@code optimizer}
56 * is called directly.
57 * @param generator Random vector generator to use for restarts.
58 * @throws NullArgumentException if {@code optimizer} or {@code generator}
59 * is {@code null}.
60 * @throws MathIllegalArgumentException if {@code starts < 1}.
61 */
62 public MultiStartMultivariateOptimizer(final MultivariateOptimizer optimizer,
63 final int starts,
64 final RandomVectorGenerator generator)
65 throws MathIllegalArgumentException, NullArgumentException {
66 super(optimizer, starts, generator);
67 this.optimizer = optimizer;
68 this.optima = new ArrayList<>();
69 }
70
71 /**
72 * {@inheritDoc}
73 */
74 @Override
75 public PointValuePair[] getOptima() {
76 Collections.sort(optima, getPairComparator());
77 return optima.toArray(new PointValuePair[0]);
78 }
79
80 /**
81 * {@inheritDoc}
82 */
83 @Override
84 protected void store(PointValuePair optimum) {
85 optima.add(optimum);
86 }
87
88 /**
89 * {@inheritDoc}
90 */
91 @Override
92 protected void clear() {
93 optima.clear();
94 }
95
96 /**
97 * @return a comparator for sorting the optima.
98 */
99 private Comparator<PointValuePair> getPairComparator() {
100 return new Comparator<PointValuePair>() {
101 /** {@inheritDoc} */
102 @Override
103 public int compare(final PointValuePair o1,
104 final PointValuePair o2) {
105 if (o1 == null) {
106 return (o2 == null) ? 0 : 1;
107 } else if (o2 == null) {
108 return -1;
109 }
110 final double v1 = o1.getValue();
111 final double v2 = o2.getValue();
112 return (optimizer.getGoalType() == GoalType.MINIMIZE) ?
113 Double.compare(v1, v2) : Double.compare(v2, v1);
114 }
115 };
116 }
117 }