001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.math4.util;
018
019import java.io.Serializable;
020
021import org.apache.commons.math4.exception.MathIllegalArgumentException;
022
023
024/**
025 * A mid point strategy based on the average of begin and end indices.
026 * @since 3.4
027 */
028public class CentralPivotingStrategy implements PivotingStrategyInterface, Serializable {
029
030    /** Serializable UID. */
031    private static final long serialVersionUID = 20140713L;
032
033    /**
034     * {@inheritDoc}
035     * This in particular picks a average of begin and end indices
036     * @return The index corresponding to a simple average of
037     * the first and the last element indices of the array slice
038     * @throws MathIllegalArgumentException when indices exceeds range
039     */
040    @Override
041    public int pivotIndex(final double[] work, final int begin, final int end)
042        throws MathIllegalArgumentException {
043        MathArrays.verifyValues(work, begin, end-begin);
044        return begin + (end - begin)/2;
045    }
046
047}