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+/*
+ * 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<T[], T[]>> pointsAndWeights
+ = new TreeMap<Integer, Pair<T[], T[]>>();
+ /** Cache for double-precision rules. */
+ private final Map<Integer, Pair<double[], double[]>> pointsAndWeightsDouble
+ = new TreeMap<Integer, Pair<double[], double[]>>();
+
+ /**
+ * 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<double[], double[]> convertToDouble(Pair<T[], T[]> 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);
+ }
+}