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.math4.legacy.analysis.function;
19
20 import java.util.Arrays;
21
22 import org.apache.commons.math4.legacy.analysis.UnivariateFunction;
23 import org.apache.commons.math4.legacy.exception.DimensionMismatchException;
24 import org.apache.commons.math4.legacy.exception.NoDataException;
25 import org.apache.commons.math4.legacy.exception.NonMonotonicSequenceException;
26 import org.apache.commons.math4.legacy.exception.NullArgumentException;
27 import org.apache.commons.math4.legacy.core.MathArrays;
28
29 /**
30 * <a href="http://en.wikipedia.org/wiki/Step_function">
31 * Step function</a>.
32 *
33 * @since 3.0
34 */
35 public class StepFunction implements UnivariateFunction {
36 /** Abscissae. */
37 private final double[] abscissa;
38 /** Ordinates. */
39 private final double[] ordinate;
40
41 /**
42 * Builds a step function from a list of arguments and the corresponding
43 * values. Specifically, returns the function h(x) defined by <pre><code>
44 * h(x) = y[0] for all x < x[1]
45 * y[1] for x[1] ≤ x < x[2]
46 * ...
47 * y[y.length - 1] for x ≥ x[x.length - 1]
48 * </code></pre>
49 * The value of {@code x[0]} is ignored, but it must be strictly less than
50 * {@code x[1]}.
51 *
52 * @param x Domain values where the function changes value.
53 * @param y Values of the function.
54 * @throws NonMonotonicSequenceException
55 * if the {@code x} array is not sorted in strictly increasing order.
56 * @throws NullArgumentException if {@code x} or {@code y} are {@code null}.
57 * @throws NoDataException if {@code x} or {@code y} are zero-length.
58 * @throws DimensionMismatchException if {@code x} and {@code y} do not
59 * have the same length.
60 */
61 public StepFunction(double[] x,
62 double[] y)
63 throws NullArgumentException, NoDataException,
64 DimensionMismatchException, NonMonotonicSequenceException {
65 if (x == null ||
66 y == null) {
67 throw new NullArgumentException();
68 }
69 if (x.length == 0 ||
70 y.length == 0) {
71 throw new NoDataException();
72 }
73 if (y.length != x.length) {
74 throw new DimensionMismatchException(y.length, x.length);
75 }
76 MathArrays.checkOrder(x);
77
78 abscissa = Arrays.copyOf(x, x.length);
79 ordinate = Arrays.copyOf(y, y.length);
80 }
81
82 /** {@inheritDoc} */
83 @Override
84 public double value(double x) {
85 int index = Arrays.binarySearch(abscissa, x);
86 double fx = 0;
87
88 if (index < -1) {
89 // "x" is between "abscissa[-index-2]" and "abscissa[-index-1]".
90 fx = ordinate[-index-2];
91 } else if (index >= 0) {
92 // "x" is exactly "abscissa[index]".
93 fx = ordinate[index];
94 } else {
95 // Otherwise, "x" is smaller than the first value in "abscissa"
96 // (hence the returned value should be "ordinate[0]").
97 fx = ordinate[0];
98 }
99
100 return fx;
101 }
102 }