/*
 * 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.math.linear;

/**
 * Interface defining a visitor for matrix entries.
 * 
 * @see DefaultRealMatrixChangingVisitor
 * @version $Revision$ $Date$
 * @since 2.0
 */
public interface RealMatrixChangingVisitor {

	/**
	 * Start visiting a matrix.
	 * <p>
	 * This method is called once before any entry of the matrix is visited.
	 * </p>
	 * 
	 * @param rows
	 *            number of rows of the matrix
	 * @param columns
	 *            number of columns of the matrix
	 * @param startRow
	 *            Initial row index
	 * @param endRow
	 *            Final row index (inclusive)
	 * @param startColumn
	 *            Initial column index
	 * @param endColumn
	 *            Final column index (inclusive)
	 */
	void start(int rows, int columns, int startRow, int endRow, int startColumn, int endColumn);

	/**
	 * Visit one matrix entry.
	 * 
	 * @param row
	 *            row index of the entry
	 * @param column
	 *            column index of the entry
	 * @param value
	 *            current value of the entry
	 * @return the new value to be set for the entry
	 * @throws MatrixVisitorException
	 *             if something wrong occurs
	 */
	double visit(int row, int column, double value) throws MatrixVisitorException;

	/**
	 * End visiting a matrix.
	 * <p>
	 * This method is called once after all entries of the matrix have been
	 * visited.
	 * </p>
	 * 
	 * @return the value that the <code>walkInXxxOrder</code> must return
	 */
	double end();

}
