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.NumberIsTooSmallException; 023 024 /** 025 * Adapter for classes implementing the {@link UnivariateInterpolator} 026 * interface. 027 * The data to be interpolated is assumed to be periodic. Thus values that are 028 * outside of the range can be passed to the interpolation function: They will 029 * be wrapped into the initial range before being passed to the class that 030 * actually computes the interpolation. 031 * 032 * @version $Id: UnivariatePeriodicInterpolator.java 1379904 2012-09-01 23:54:52Z erans $ 033 */ 034 public class UnivariatePeriodicInterpolator 035 implements UnivariateInterpolator { 036 /** Default number of extension points of the samples array. */ 037 public static final int DEFAULT_EXTEND = 5; 038 /** Interpolator. */ 039 private final UnivariateInterpolator interpolator; 040 /** Period. */ 041 private final double period; 042 /** Number of extension points. */ 043 private final int extend; 044 045 /** 046 * Builds an interpolator. 047 * 048 * @param interpolator Interpolator. 049 * @param period Period. 050 * @param extend Number of points to be appended at the beginning and 051 * end of the sample arrays in order to avoid interpolation failure at 052 * the (periodic) boundaries of the orginal interval. The value is the 053 * number of sample points which the original {@code interpolator} needs 054 * on each side of the interpolated point. 055 */ 056 public UnivariatePeriodicInterpolator(UnivariateInterpolator interpolator, 057 double period, 058 int extend) { 059 this.interpolator = interpolator; 060 this.period = period; 061 this.extend = extend; 062 } 063 064 /** 065 * Builds an interpolator. 066 * Uses {@link #DEFAULT_EXTEND} as the number of extension points on each side 067 * of the original abscissae range. 068 * 069 * @param interpolator Interpolator. 070 * @param period Period. 071 */ 072 public UnivariatePeriodicInterpolator(UnivariateInterpolator interpolator, 073 double period) { 074 this(interpolator, period, DEFAULT_EXTEND); 075 } 076 077 /** 078 * {@inheritDoc} 079 * 080 * @throws NumberIsTooSmallException if the number of extension points 081 * iss larger then the size of {@code xval}. 082 */ 083 public UnivariateFunction interpolate(double[] xval, 084 double[] yval) 085 throws NumberIsTooSmallException { 086 if (xval.length < extend) { 087 throw new NumberIsTooSmallException(xval.length, extend, true); 088 } 089 090 MathArrays.checkOrder(xval); 091 final double offset = xval[0]; 092 093 final int len = xval.length + extend * 2; 094 final double[] x = new double[len]; 095 final double[] y = new double[len]; 096 for (int i = 0; i < xval.length; i++) { 097 final int index = i + extend; 098 x[index] = MathUtils.reduce(xval[i], period, offset); 099 y[index] = yval[i]; 100 } 101 102 // Wrap to enable interpolation at the boundaries. 103 for (int i = 0; i < extend; i++) { 104 int index = xval.length - extend + i; 105 x[i] = MathUtils.reduce(xval[index], period, offset) - period; 106 y[i] = yval[index]; 107 108 index = len - extend + i; 109 x[index] = MathUtils.reduce(xval[i], period, offset) + period; 110 y[index] = yval[i]; 111 } 112 113 MathArrays.sortInPlace(x, y); 114 115 final UnivariateFunction f = interpolator.interpolate(x, y); 116 return new UnivariateFunction() { 117 public double value(final double x) { 118 return f.value(MathUtils.reduce(x, period, offset)); 119 } 120 }; 121 } 122 }