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diff --git a/src/main/java/org/apache/commons/math3/linear/RealMatrixPreservingVisitor.java b/src/main/java/org/apache/commons/math3/linear/RealMatrixPreservingVisitor.java
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+/*
+ * 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.math3.linear;
+
+/**
+ * Interface defining a visitor for matrix entries.
+ *
+ * @see DefaultRealMatrixPreservingVisitor
+ * @since 2.0
+ */
+public interface RealMatrixPreservingVisitor {
+    /**
+     * Start visiting a matrix.
+     *
+     * <p>This method is called once before any entry of the matrix is visited.
+     *
+     * @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
+     */
+    void visit(int row, int column, double value);
+
+    /**
+     * End visiting a matrix.
+     *
+     * <p>This method is called once after all entries of the matrix have been visited.
+     *
+     * @return the value that the <code>walkInXxxOrder</code> must return
+     */
+    double end();
+}