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The Apache Commons Math project is a library of lightweight, self-contained mathematics and statistics components addressing the most common practical problems not immediately available in the Java programming language or commons-lang.
/*
* 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.util;
import java.io.Serializable;
import org.apache.commons.math3.exception.MathIllegalArgumentException;
/**
* Classic median of 3 strategy given begin and end indices.
* @since 3.4
*/
public class MedianOf3PivotingStrategy implements PivotingStrategyInterface, Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 20140713L;
/**{@inheritDoc}
* This in specific makes use of median of 3 pivoting.
* @return The index corresponding to a pivot chosen between the
* first, middle and the last indices of the array slice
* @throws MathIllegalArgumentException when indices exceeds range
*/
public int pivotIndex(final double[] work, final int begin, final int end)
throws MathIllegalArgumentException {
MathArrays.verifyValues(work, begin, end-begin);
final int inclusiveEnd = end - 1;
final int middle = begin + (inclusiveEnd - begin) / 2;
final double wBegin = work[begin];
final double wMiddle = work[middle];
final double wEnd = work[inclusiveEnd];
if (wBegin < wMiddle) {
if (wMiddle < wEnd) {
return middle;
} else {
return wBegin < wEnd ? inclusiveEnd : begin;
}
} else {
if (wBegin < wEnd) {
return begin;
} else {
return wMiddle < wEnd ? inclusiveEnd : middle;
}
}
}
}