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diff --git a/src/main/java/org/apache/commons/math/util/DoubleArray.java b/src/main/java/org/apache/commons/math/util/DoubleArray.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.math.util;
+
+
+/**
+ * Provides a standard interface for double arrays.  Allows different
+ * array implementations to support various storage mechanisms
+ * such as automatic expansion, contraction, and array "rolling".
+ *
+ * @version $Revision: 811685 $ $Date: 2009-09-05 19:36:48 +0200 (sam. 05 sept. 2009) $
+ */
+public interface DoubleArray {
+
+    /**
+     * Returns the number of elements currently in the array.  Please note
+     * that this may be different from the length of the internal storage array.
+     *
+     * @return number of elements
+     */
+    int getNumElements();
+
+    /**
+     * Returns the element at the specified index.  Note that if an
+     * out of bounds index is supplied a ArrayIndexOutOfBoundsException
+     * will be thrown.
+     *
+     * @param index index to fetch a value from
+     * @return value stored at the specified index
+     * @throws ArrayIndexOutOfBoundsException if <code>index</code> is less than
+     *         zero or is greater than <code>getNumElements() - 1</code>.
+     */
+    double getElement(int index);
+
+    /**
+     * Sets the element at the specified index.  If the specified index is greater than
+     * <code>getNumElements() - 1</code>, the <code>numElements</code> property
+     * is increased to <code>index +1</code> and additional storage is allocated
+     * (if necessary) for the new element and all  (uninitialized) elements
+     * between the new element and the previous end of the array).
+     *
+     * @param index index to store a value in
+     * @param value value to store at the specified index
+     * @throws ArrayIndexOutOfBoundsException if <code>index</code> is less than
+     *         zero.
+     */
+    void setElement(int index, double value);
+
+    /**
+     * Adds an element to the end of this expandable array
+     *
+     * @param value to be added to end of array
+     */
+    void addElement(double value);
+
+    /**
+     * <p>
+     * Adds an element to the end of the array and removes the first
+     * element in the array.  Returns the discarded first element.
+     * The effect is similar to a push operation in a FIFO queue.
+     * </p>
+     * <p>
+     * Example: If the array contains the elements 1, 2, 3, 4 (in that order)
+     * and addElementRolling(5) is invoked, the result is an array containing
+     * the entries 2, 3, 4, 5 and the value returned is 1.
+     * </p>
+     *
+     * @param value the value to be added to the array
+     * @return the value which has been discarded or "pushed" out of the array
+     *         by this rolling insert
+     */
+    double addElementRolling(double value);
+
+    /**
+     * Returns a double[] array containing the elements of this
+     * <code>DoubleArray</code>.  If the underlying implementation is
+     * array-based, this method should always return a copy, rather than a
+     * reference to the underlying array so that changes made to the returned
+     *  array have no effect on the <code>DoubleArray.</code>
+     *
+     * @return all elements added to the array
+     */
+    double[] getElements();
+
+    /**
+     * Clear the double array
+     */
+    void clear();
+
+}