/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.math3.analysis.interpolation;
import org.apache.commons.math3.analysis.polynomials.PolynomialFunction;
import org.apache.commons.math3.analysis.polynomials.PolynomialSplineFunction;
import org.apache.commons.math3.util.MathArrays;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.NumberIsTooSmallException;
import org.apache.commons.math3.exception.NonMonotonicSequenceException;
import org.apache.commons.math3.exception.util.LocalizedFormats;
/**
* Implements a linear function for interpolation of real univariate functions.
*
*/
public class LinearInterpolator implements UnivariateInterpolator {
/**
* Computes a linear interpolating function for the data set.
*
* @param x the arguments for the interpolation points
* @param y the values for the interpolation points
* @return a function which interpolates the data set
* @throws DimensionMismatchException if {@code x} and {@code y}
* have different sizes.
* @throws NonMonotonicSequenceException if {@code x} is not sorted in
* strict increasing order.
* @throws NumberIsTooSmallException if the size of {@code x} is smaller
* than 2.
*/
public PolynomialSplineFunction interpolate(double x[], double y[])
throws DimensionMismatchException,
NumberIsTooSmallException,
NonMonotonicSequenceException {
if (x.length != y.length) {
throw new DimensionMismatchException(x.length, y.length);
}
if (x.length < 2) {
throw new NumberIsTooSmallException(LocalizedFormats.NUMBER_OF_POINTS,
x.length, 2, true);
}
// Number of intervals. The number of data points is n + 1.
int n = x.length - 1;
MathArrays.checkOrder(x);
// Slope of the lines between the datapoints.
final double m[] = new double[n];
for (int i = 0; i < n; i++) {
m[i] = (y[i + 1] - y[i]) / (x[i + 1] - x[i]);
}
final PolynomialFunction polynomials[] = new PolynomialFunction[n];
final double coefficients[] = new double[2];
for (int i = 0; i < n; i++) {
coefficients[0] = y[i];
coefficients[1] = m[i];
polynomials[i] = new PolynomialFunction(coefficients);
}
return new PolynomialSplineFunction(x, polynomials);
}
}