Github user chiwanpark commented on a diff in the pull request:
https://github.com/apache/flink/pull/629#discussion_r29838750
--- Diff: flink-staging/flink-ml/src/main/scala/org/apache/flink/ml/math/metrics/distances/CosineDistanceMeasure.scala ---
@@ -0,0 +1,45 @@
+/*
+ * 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.flink.ml.math.metrics.distances
+
+import org.apache.flink.ml.math.Vector
+
+/** This class implements a cosine distance metric. The class calculates the distance between
+ * the given vectors by dividing the dot product of two vectors by the product of their lengths.
+ * We convert the result of division to a usable distance. So, 1 - cos(angle) is actually returned.
+ *
+ * @see http://en.wikipedia.org/wiki/Cosine_similarity
+ */
+class CosineDistanceMeasure extends DistanceMeasure {
+ override def distance(a: Vector, b: Vector): Double = {
+ checkValidArguments(a, b)
+
+ val dotProd: Double = a.dot(b)
+ val denominator: Double = a.magnitude * b.magnitude
+ if (dotProd == 0 && denominator == 0) {
--- End diff --
No. If `a` and `b` are both zero, they are similar. The zero distance means exactly same.
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