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.linear;
018
019/**
020 * This interface defines a visitor for the entries of a vector. Visitors
021 * implementing this interface may alter the entries of the vector being
022 * visited.
023 *
024 * @since 3.1
025 */
026public interface RealVectorChangingVisitor {
027    /**
028     * Start visiting a vector. This method is called once, before any entry
029     * of the vector is visited.
030     *
031     * @param dimension the size of the vector
032     * @param start the index of the first entry to be visited
033     * @param end the index of the last entry to be visited (inclusive)
034     */
035    void start(int dimension, int start, int end);
036
037    /**
038     * Visit one entry of the vector.
039     *
040     * @param index the index of the entry being visited
041     * @param value the value of the entry being visited
042     * @return the new value of the entry being visited
043     */
044    double visit(int index, double value);
045
046    /**
047     * End visiting a vector. This method is called once, after all entries of
048     * the vector have been visited.
049     *
050     * @return the value returned by
051     * {@link RealVector#walkInDefaultOrder(RealVectorChangingVisitor)},
052     * {@link RealVector#walkInDefaultOrder(RealVectorChangingVisitor, int, int)},
053     * {@link RealVector#walkInOptimizedOrder(RealVectorChangingVisitor)}
054     * or
055     * {@link RealVector#walkInOptimizedOrder(RealVectorChangingVisitor, int, int)}
056     */
057    double end();
058}