Github user gallenvara commented on a diff in the pull request:
https://github.com/apache/flink/pull/1956#discussion_r61772427
 Diff: flinklibraries/flinkgelly/src/main/java/org/apache/flink/graph/library/HITSAlgorithm.java

@@ 0,0 +1,194 @@
+/*
+ * 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/LICENSE2.0
+ *
+ * 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.graph.library;
+
+import org.apache.flink.api.common.aggregators.DoubleSumAggregator;
+import org.apache.flink.api.java.DataSet;
+
+import org.apache.flink.graph.Edge;
+import org.apache.flink.graph.EdgeDirection;
+import org.apache.flink.graph.Graph;
+import org.apache.flink.graph.GraphAlgorithm;
+import org.apache.flink.graph.Vertex;
+import org.apache.flink.graph.spargel.MessageIterator;
+import org.apache.flink.graph.spargel.MessagingFunction;
+import org.apache.flink.graph.spargel.ScatterGatherConfiguration;
+import org.apache.flink.graph.spargel.VertexUpdateFunction;
+import org.apache.flink.types.DoubleValue;
+
+/**
+ * This is an implementation of HITS algorithm, using a scattergather iteration.
+ * The user can define the maximum number of iterations. HITS algorithm is determined
by two parameters,
+ * hubs and authorities. A good hub represented a page that pointed to many other pages,
and a good authority
+ * represented a page that was linked by many different hubs. The implementation assumes
that the two value on
+ * every vertex are the same at the beginning.
+ * <p>
+ * If the number of vertices of the input graph is known, it should be provided as a
parameter
+ * to speed up computation. Otherwise, the algorithm will first execute a job to count
the vertices.
+ */
+public class HITSAlgorithm<K> implements GraphAlgorithm<K, Double, Double, DataSet<Vertex<K,
Double>>> {
+
+ public static enum HITSParameter {
+ HUB,
+ AUTHORITY
+ }
+
+ private int maxIterations;
+ private long numberOfVertices;
+
+ /**
+ * Creates an instance of HITS algorithm.
+ * If the number of vertices of the input graph is known,
+ * use the {@link HITSAlgorithm#HITSAlgorithm(int, long, HITSParameter)} constructor
instead.
+ *
+ * @param maxIterations the maximum number of iterations
+ * @param hitsParameter the type of final web pages users want to get by this algorithm
+ */
+ public HITSAlgorithm(int maxIterations, HITSParameter hitsParameter) {
+ if (hitsParameter == HITSParameter.AUTHORITY) {
+ this.maxIterations = maxIterations * 2;
+ } else {
+ this.maxIterations = maxIterations * 2 + 1;
+ }
+ }
+
+ /**
+ * Creates an instance of HITS algorithm.
+ * If the number of vertices of the input graph is unknown,
+ * use the {@link HITSAlgorithm#HITSAlgorithm(int, HITSParameter)} constructor instead.
+ *
+ * @param maxIterations the maximum number of iterations
+ * @param hitsParameter the type of final web pages users want to get by this algorithm
+ */
+ public HITSAlgorithm(int maxIterations, long numberOfVertices, HITSParameter hitsParameter)
{
+ if (hitsParameter == HITSParameter.AUTHORITY) {
+ this.maxIterations = maxIterations * 2;
+ } else {
+ this.maxIterations = maxIterations * 2 + 1;
+ }
+ this.numberOfVertices = numberOfVertices;
+ }
+
+ @Override
+ public DataSet<Vertex<K, Double>> run(Graph<K, Double, Double> netGraph)
throws Exception {
 End diff 
The two phases are depended on each other. Hub can update until authority updated and
normalized, also the same to authority. So the two updating processing is in a front and back
order, i mean they are belong to different iteration step. Return a `tuple2` value means that
we can get hub and authority in the same `superstep`. So the `HITSParameter` being set.

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