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 }