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.polynomials.PolynomialFunction;
020 import org.apache.commons.math3.analysis.polynomials.PolynomialSplineFunction;
021 import org.apache.commons.math3.util.MathArrays;
022 import org.apache.commons.math3.exception.DimensionMismatchException;
023 import org.apache.commons.math3.exception.NumberIsTooSmallException;
024 import org.apache.commons.math3.exception.NonMonotonicSequenceException;
025 import org.apache.commons.math3.exception.util.LocalizedFormats;
026
027 /**
028 * Implements a linear function for interpolation of real univariate functions.
029 *
030 * @version $Id: LinearInterpolator.java 1379904 2012-09-01 23:54:52Z erans $
031 */
032 public class LinearInterpolator implements UnivariateInterpolator {
033 /**
034 * Computes a linear interpolating function for the data set.
035 *
036 * @param x the arguments for the interpolation points
037 * @param y the values for the interpolation points
038 * @return a function which interpolates the data set
039 * @throws DimensionMismatchException if {@code x} and {@code y}
040 * have different sizes.
041 * @throws NonMonotonicSequenceException if {@code x} is not sorted in
042 * strict increasing order.
043 * @throws NumberIsTooSmallException if the size of {@code x} is smaller
044 * than 2.
045 */
046 public PolynomialSplineFunction interpolate(double x[], double y[])
047 throws DimensionMismatchException,
048 NumberIsTooSmallException,
049 NonMonotonicSequenceException {
050 if (x.length != y.length) {
051 throw new DimensionMismatchException(x.length, y.length);
052 }
053
054 if (x.length < 2) {
055 throw new NumberIsTooSmallException(LocalizedFormats.NUMBER_OF_POINTS,
056 x.length, 2, true);
057 }
058
059 // Number of intervals. The number of data points is n + 1.
060 int n = x.length - 1;
061
062 MathArrays.checkOrder(x);
063
064 // Slope of the lines between the datapoints.
065 final double m[] = new double[n];
066 for (int i = 0; i < n; i++) {
067 m[i] = (y[i + 1] - y[i]) / (x[i + 1] - x[i]);
068 }
069
070 final PolynomialFunction polynomials[] = new PolynomialFunction[n];
071 final double coefficients[] = new double[2];
072 for (int i = 0; i < n; i++) {
073 coefficients[0] = y[i];
074 coefficients[1] = m[i];
075 polynomials[i] = new PolynomialFunction(coefficients);
076 }
077
078 return new PolynomialSplineFunction(x, polynomials);
079 }
080 }