001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.commons.math3.analysis.interpolation;
018
019 import org.apache.commons.math3.analysis.UnivariateFunction;
020 import org.apache.commons.math3.util.MathUtils;
021 import org.apache.commons.math3.util.MathArrays;
022 import org.apache.commons.math3.exception.MathIllegalArgumentException;
023 import org.apache.commons.math3.exception.NonMonotonicSequenceException;
024 import org.apache.commons.math3.exception.NumberIsTooSmallException;
025
026 /**
027 * Adapter for classes implementing the {@link UnivariateInterpolator}
028 * interface.
029 * The data to be interpolated is assumed to be periodic. Thus values that are
030 * outside of the range can be passed to the interpolation function: They will
031 * be wrapped into the initial range before being passed to the class that
032 * actually computes the interpolation.
033 *
034 * @version $Id: UnivariatePeriodicInterpolator.java 1459739 2013-03-22 11:58:11Z erans $
035 */
036 public class UnivariatePeriodicInterpolator
037 implements UnivariateInterpolator {
038 /** Default number of extension points of the samples array. */
039 public static final int DEFAULT_EXTEND = 5;
040 /** Interpolator. */
041 private final UnivariateInterpolator interpolator;
042 /** Period. */
043 private final double period;
044 /** Number of extension points. */
045 private final int extend;
046
047 /**
048 * Builds an interpolator.
049 *
050 * @param interpolator Interpolator.
051 * @param period Period.
052 * @param extend Number of points to be appended at the beginning and
053 * end of the sample arrays in order to avoid interpolation failure at
054 * the (periodic) boundaries of the orginal interval. The value is the
055 * number of sample points which the original {@code interpolator} needs
056 * on each side of the interpolated point.
057 */
058 public UnivariatePeriodicInterpolator(UnivariateInterpolator interpolator,
059 double period,
060 int extend) {
061 this.interpolator = interpolator;
062 this.period = period;
063 this.extend = extend;
064 }
065
066 /**
067 * Builds an interpolator.
068 * Uses {@link #DEFAULT_EXTEND} as the number of extension points on each side
069 * of the original abscissae range.
070 *
071 * @param interpolator Interpolator.
072 * @param period Period.
073 */
074 public UnivariatePeriodicInterpolator(UnivariateInterpolator interpolator,
075 double period) {
076 this(interpolator, period, DEFAULT_EXTEND);
077 }
078
079 /**
080 * {@inheritDoc}
081 *
082 * @throws NumberIsTooSmallException if the number of extension points
083 * is larger than the size of {@code xval}.
084 */
085 public UnivariateFunction interpolate(double[] xval,
086 double[] yval)
087 throws NumberIsTooSmallException, NonMonotonicSequenceException {
088 if (xval.length < extend) {
089 throw new NumberIsTooSmallException(xval.length, extend, true);
090 }
091
092 MathArrays.checkOrder(xval);
093 final double offset = xval[0];
094
095 final int len = xval.length + extend * 2;
096 final double[] x = new double[len];
097 final double[] y = new double[len];
098 for (int i = 0; i < xval.length; i++) {
099 final int index = i + extend;
100 x[index] = MathUtils.reduce(xval[i], period, offset);
101 y[index] = yval[i];
102 }
103
104 // Wrap to enable interpolation at the boundaries.
105 for (int i = 0; i < extend; i++) {
106 int index = xval.length - extend + i;
107 x[i] = MathUtils.reduce(xval[index], period, offset) - period;
108 y[i] = yval[index];
109
110 index = len - extend + i;
111 x[index] = MathUtils.reduce(xval[i], period, offset) + period;
112 y[index] = yval[i];
113 }
114
115 MathArrays.sortInPlace(x, y);
116
117 final UnivariateFunction f = interpolator.interpolate(x, y);
118 return new UnivariateFunction() {
119 public double value(final double x) throws MathIllegalArgumentException {
120 return f.value(MathUtils.reduce(x, period, offset));
121 }
122 };
123 }
124 }