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.math.analysis.interpolation; 018 019 import org.apache.commons.math.exception.DimensionMismatchException; 020 import org.apache.commons.math.exception.util.LocalizedFormats; 021 import org.apache.commons.math.exception.NumberIsTooSmallException; 022 import org.apache.commons.math.analysis.polynomials.PolynomialFunction; 023 import org.apache.commons.math.analysis.polynomials.PolynomialSplineFunction; 024 import org.apache.commons.math.util.MathUtils; 025 026 /** 027 * Implements a linear function for interpolation of real univariate functions. 028 * @version $Revision$ $Date$ 029 * @since 2.2 030 */ 031 public class LinearInterpolator implements UnivariateRealInterpolator { 032 /** 033 * Computes a linear interpolating function for the data set. 034 * @param x the arguments for the interpolation points 035 * @param y the values for the interpolation points 036 * @return a function which interpolates the data set 037 * @throws DimensionMismatchException if {@code x} and {@code y} 038 * have different sizes. 039 * @throws org.apache.commons.math.exception.NonMonotonousSequenceException 040 * if {@code x} is not sorted in strict increasing order. 041 * @throws NumberIsTooSmallException if the size of {@code x} is smaller 042 * than 2. 043 */ 044 public PolynomialSplineFunction interpolate(double x[], double y[]) { 045 if (x.length != y.length) { 046 throw new DimensionMismatchException(x.length, y.length); 047 } 048 049 if (x.length < 2) { 050 throw new NumberIsTooSmallException(LocalizedFormats.NUMBER_OF_POINTS, 051 x.length, 2, true); 052 } 053 054 // Number of intervals. The number of data points is n + 1. 055 int n = x.length - 1; 056 057 MathUtils.checkOrder(x); 058 059 // Slope of the lines between the datapoints. 060 final double m[] = new double[n]; 061 for (int i = 0; i < n; i++) { 062 m[i] = (y[i + 1] - y[i]) / (x[i + 1] - x[i]); 063 } 064 065 PolynomialFunction polynomials[] = new PolynomialFunction[n]; 066 final double coefficients[] = new double[2]; 067 for (int i = 0; i < n; i++) { 068 coefficients[0] = y[i]; 069 coefficients[1] = m[i]; 070 polynomials[i] = new PolynomialFunction(coefficients); 071 } 072 073 return new PolynomialSplineFunction(x, polynomials); 074 } 075 }