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diff --git a/src/main/java/org/apache/commons/math3/stat/ranking/RankingAlgorithm.java b/src/main/java/org/apache/commons/math3/stat/ranking/RankingAlgorithm.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.stat.ranking;
+
+/**
+ * Interface representing a rank transformation.
+ *
+ * @since 2.0
+ */
+public interface RankingAlgorithm {
+    /**
+     * <p>Performs a rank transformation on the input data, returning an array
+     * of ranks.</p>
+     *
+     * <p>Ranks should be 1-based - that is, the smallest value
+     * returned in an array of ranks should be greater than or equal to one,
+     * rather than 0. Ranks should in general take integer values, though
+     * implementations may return averages or other floating point values
+     * to resolve ties in the input data.</p>
+     *
+     * @param data array of data to be ranked
+     * @return an array of ranks corresponding to the elements of the input array
+     */
+    double[] rank (double[] data);
+}