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
23 package org.hipparchus.analysis.function;
24
25 import java.util.Arrays;
26
27 import org.hipparchus.analysis.UnivariateFunction;
28 import org.hipparchus.exception.LocalizedCoreFormats;
29 import org.hipparchus.exception.MathIllegalArgumentException;
30 import org.hipparchus.exception.NullArgumentException;
31 import org.hipparchus.util.MathArrays;
32
33 /**
34 * <a href="http://en.wikipedia.org/wiki/Step_function">
35 * Step function</a>.
36 *
37 */
38 public class StepFunction implements UnivariateFunction {
39 /** Abscissae. */
40 private final double[] abscissa;
41 /** Ordinates. */
42 private final double[] ordinate;
43
44 /**
45 * Builds a step function from a list of arguments and the corresponding
46 * values. Specifically, returns the function h(x) defined by <pre><code>
47 * h(x) = y[0] for all x < x[1]
48 * y[1] for x[1] ≤ x < x[2]
49 * ...
50 * y[y.length - 1] for x ≥ x[x.length - 1]
51 * </code></pre>
52 * The value of {@code x[0]} is ignored, but it must be strictly less than
53 * {@code x[1]}.
54 *
55 * @param x Domain values where the function changes value.
56 * @param y Values of the function.
57 * @throws MathIllegalArgumentException
58 * if the {@code x} array is not sorted in strictly increasing order.
59 * @throws NullArgumentException if {@code x} or {@code y} are {@code null}.
60 * @throws MathIllegalArgumentException if {@code x} or {@code y} are zero-length.
61 * @throws MathIllegalArgumentException if {@code x} and {@code y} do not
62 * have the same length.
63 */
64 public StepFunction(double[] x,
65 double[] y)
66 throws MathIllegalArgumentException, NullArgumentException {
67 if (x == null ||
68 y == null) {
69 throw new NullArgumentException();
70 }
71 if (x.length == 0 ||
72 y.length == 0) {
73 throw new MathIllegalArgumentException(LocalizedCoreFormats.NO_DATA);
74 }
75 MathArrays.checkEqualLength(y, x);
76 MathArrays.checkOrder(x);
77
78 abscissa = x.clone();
79 ordinate = y.clone();
80 }
81
82 /** {@inheritDoc} */
83 @Override
84 public double value(double x) {
85 final int index = Arrays.binarySearch(abscissa, x);
86
87 if (index < -1) {
88 // "x" is between "abscissa[-index-2]" and "abscissa[-index-1]".
89 return ordinate[-index-2];
90 } else if (index >= 0) {
91 // "x" is exactly "abscissa[index]".
92 return ordinate[index];
93 } else {
94 // Otherwise, "x" is smaller than the first value in "abscissa"
95 // (hence the returned value should be "ordinate[0]").
96 return ordinate[0];
97 }
98
99 }
100 }