/*
 * 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.math4.linear;

/**
 * This interface defines a visitor for the entries of a vector. Visitors
 * implementing this interface may alter the entries of the vector being
 * visited.
 *
 * @since 3.1
 */
public interface RealVectorChangingVisitor {
    /**
     * Start visiting a vector. This method is called once, before any entry
     * of the vector is visited.
     *
     * @param dimension the size of the vector
     * @param start the index of the first entry to be visited
     * @param end the index of the last entry to be visited (inclusive)
     */
    void start(int dimension, int start, int end);

    /**
     * Visit one entry of the vector.
     *
     * @param index the index of the entry being visited
     * @param value the value of the entry being visited
     * @return the new value of the entry being visited
     */
    double visit(int index, double value);

    /**
     * End visiting a vector. This method is called once, after all entries of
     * the vector have been visited.
     *
     * @return the value returned by
     * {@link RealVector#walkInDefaultOrder(RealVectorChangingVisitor)},
     * {@link RealVector#walkInDefaultOrder(RealVectorChangingVisitor, int, int)},
     * {@link RealVector#walkInOptimizedOrder(RealVectorChangingVisitor)}
     * or
     * {@link RealVector#walkInOptimizedOrder(RealVectorChangingVisitor, int, int)}
     */
    double end();
}