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Java example source code file (SymmetricGaussIntegrator.java)

This example Java source code file (SymmetricGaussIntegrator.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

dimensionmismatchexception, gaussintegrator, nonmonotonicsequenceexception, override, symmetricgaussintegrator

The SymmetricGaussIntegrator.java Java example source code

 * 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,
 * See the License for the specific language governing permissions and
 * limitations under the License.
package org.apache.commons.math3.analysis.integration.gauss;

import org.apache.commons.math3.analysis.UnivariateFunction;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.NonMonotonicSequenceException;
import org.apache.commons.math3.util.Pair;

 * This class's implements {@link #integrate(UnivariateFunction) integrate}
 * method assuming that the integral is symmetric about 0.
 * This allows to reduce numerical errors.
 * @since 3.3
public class SymmetricGaussIntegrator extends GaussIntegrator {
     * Creates an integrator from the given {@code points} and {@code weights}.
     * The integration interval is defined by the first and last value of
     * {@code points} which must be sorted in increasing order.
     * @param points Integration points.
     * @param weights Weights of the corresponding integration nodes.
     * @throws NonMonotonicSequenceException if the {@code points} are not
     * sorted in increasing order.
     * @throws DimensionMismatchException if points and weights don't have the same length
    public SymmetricGaussIntegrator(double[] points,
                                    double[] weights)
        throws NonMonotonicSequenceException, DimensionMismatchException {
        super(points, weights);

     * Creates an integrator from the given pair of points (first element of
     * the pair) and weights (second element of the pair.
     * @param pointsAndWeights Integration points and corresponding weights.
     * @throws NonMonotonicSequenceException if the {@code points} are not
     * sorted in increasing order.
     * @see #SymmetricGaussIntegrator(double[], double[])
    public SymmetricGaussIntegrator(Pair<double[], double[]> pointsAndWeights)
        throws NonMonotonicSequenceException {
        this(pointsAndWeights.getFirst(), pointsAndWeights.getSecond());

     * {@inheritDoc}
    public double integrate(UnivariateFunction f) {
        final int ruleLength = getNumberOfPoints();

        if (ruleLength == 1) {
            return getWeight(0) * f.value(0d);

        final int iMax = ruleLength / 2;
        double s = 0;
        double c = 0;
        for (int i = 0; i < iMax; i++) {
            final double p = getPoint(i);
            final double w = getWeight(i);

            final double f1 = f.value(p);
            final double f2 = f.value(-p);

            final double y = w * (f1 + f2) - c;
            final double t = s + y;

            c = (t - s) - y;
            s = t;

        if (ruleLength % 2 != 0) {
            final double w = getWeight(iMax);

            final double y = w * f.value(0d) - c;
            final double t = s + y;

            s = t;

        return s;

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