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Java example source code file (BaseRuleFactory.java)

This example Java source code file (BaseRuleFactory.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.

Learn more about this Java project at its project page.

Java - Java tags/keywords

baserulefactory, dimensionmismatchexception, notstrictlypositiveexception, number, pair, treemap, util

The BaseRuleFactory.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,
 * 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.integration.gauss;

import java.util.Map;
import java.util.TreeMap;
import org.apache.commons.math3.util.Pair;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.NotStrictlyPositiveException;
import org.apache.commons.math3.exception.util.LocalizedFormats;

/**
 * Base class for rules that determines the integration nodes and their
 * weights.
 * Subclasses must implement the {@link #computeRule(int) computeRule} method.
 *
 * @param <T> Type of the number used to represent the points and weights of
 * the quadrature rules.
 *
 * @since 3.1
 */
public abstract class BaseRuleFactory<T extends Number> {
    /** List of points and weights, indexed by the order of the rule. */
    private final Map<Integer, Pair pointsAndWeights
        = new TreeMap<Integer, Pair();
    /** Cache for double-precision rules. */
    private final Map<Integer, Pair pointsAndWeightsDouble
        = new TreeMap<Integer, Pair();

    /**
     * Gets a copy of the quadrature rule with the given number of integration
     * points.
     *
     * @param numberOfPoints Number of integration points.
     * @return a copy of the integration rule.
     * @throws NotStrictlyPositiveException if {@code numberOfPoints < 1}.
     * @throws DimensionMismatchException if the elements of the rule pair do not
     * have the same length.
     */
    public Pair<double[], double[]> getRule(int numberOfPoints)
        throws NotStrictlyPositiveException, DimensionMismatchException {

        if (numberOfPoints <= 0) {
            throw new NotStrictlyPositiveException(LocalizedFormats.NUMBER_OF_POINTS,
                                                   numberOfPoints);
        }

        // Try to obtain the rule from the cache.
        Pair<double[], double[]> cached = pointsAndWeightsDouble.get(numberOfPoints);

        if (cached == null) {
            // Rule not computed yet.

            // Compute the rule.
            final Pair<T[], T[]> rule = getRuleInternal(numberOfPoints);
            cached = convertToDouble(rule);

            // Cache it.
            pointsAndWeightsDouble.put(numberOfPoints, cached);
        }

        // Return a copy.
        return new Pair<double[], double[]>(cached.getFirst().clone(),
                                            cached.getSecond().clone());
    }

    /**
     * Gets a rule.
     * Synchronization ensures that rules will be computed and added to the
     * cache at most once.
     * The returned rule is a reference into the cache.
     *
     * @param numberOfPoints Order of the rule to be retrieved.
     * @return the points and weights corresponding to the given order.
     * @throws DimensionMismatchException if the elements of the rule pair do not
     * have the same length.
     */
    protected synchronized Pair<T[], T[]> getRuleInternal(int numberOfPoints)
        throws DimensionMismatchException {
        final Pair<T[], T[]> rule = pointsAndWeights.get(numberOfPoints);
        if (rule == null) {
            addRule(computeRule(numberOfPoints));
            // The rule should be available now.
            return getRuleInternal(numberOfPoints);
        }
        return rule;
    }

    /**
     * Stores a rule.
     *
     * @param rule Rule to be stored.
     * @throws DimensionMismatchException if the elements of the pair do not
     * have the same length.
     */
    protected void addRule(Pair<T[], T[]> rule) throws DimensionMismatchException {
        if (rule.getFirst().length != rule.getSecond().length) {
            throw new DimensionMismatchException(rule.getFirst().length,
                                                 rule.getSecond().length);
        }

        pointsAndWeights.put(rule.getFirst().length, rule);
    }

    /**
     * Computes the rule for the given order.
     *
     * @param numberOfPoints Order of the rule to be computed.
     * @return the computed rule.
     * @throws DimensionMismatchException if the elements of the pair do not
     * have the same length.
     */
    protected abstract Pair<T[], T[]> computeRule(int numberOfPoints)
        throws DimensionMismatchException;

    /**
     * Converts the from the actual {@code Number} type to {@code double}
     *
     * @param <T> Type of the number used to represent the points and
     * weights of the quadrature rules.
     * @param rule Points and weights.
     * @return points and weights as {@code double}s.
     */
    private static <T extends Number> Pair convertToDouble(Pair rule) {
        final T[] pT = rule.getFirst();
        final T[] wT = rule.getSecond();

        final int len = pT.length;
        final double[] pD = new double[len];
        final double[] wD = new double[len];

        for (int i = 0; i < len; i++) {
            pD[i] = pT[i].doubleValue();
            wD[i] = wT[i].doubleValue();
        }

        return new Pair<double[], double[]>(pD, wD);
    }
}

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