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 org.apache.commons.math4.exception.MathIllegalArgumentException;
020
021
022/**
023 * A strategy to pick a pivoting index of an array for doing partitioning.
024 * @see MedianOf3PivotingStrategy
025 * @see RandomPivotingStrategy
026 * @see CentralPivotingStrategy
027 * @since 3.4
028 */
029public interface PivotingStrategyInterface {
030
031    /**
032     * Find pivot index of the array so that partition and K<sup>th</sup>
033     * element selection can be made
034     * @param work data array
035     * @param begin index of the first element of the slice
036     * @param end index after the last element of the slice
037     * @return the index of the pivot element chosen between the
038     * first and the last element of the array slice
039     * @throws MathIllegalArgumentException when indices exceeds range
040     */
041    int pivotIndex(double[] work, int begin, int end)
042        throws MathIllegalArgumentException;
043
044}