Github user gallenvara commented on a diff in the pull request:
https://github.com/apache/flink/pull/1956#discussion_r62514639
--- Diff:
flink-libraries/flink-gelly/src/main/java/org/apache/flink/graph/library/HITSAlgorithm.java
---
@@ -0,0 +1,183 @@
+/*
+ * 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.graph.library;
+
+import org.apache.flink.api.common.aggregators.DoubleSumAggregator;
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.api.java.DataSet;
+
+import org.apache.flink.api.java.tuple.Tuple2;
+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.graph.utils.NullValueEdgeMapper;
+import org.apache.flink.types.DoubleValue;
+import org.apache.flink.types.NullValue;
+import org.apache.flink.util.Preconditions;
+
+/**
+ * This is an implementation of HITS algorithm, using a scatter-gather
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.
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/HITS_algorithm";>HITS
Algorithm</a>
+ */
+public class HITSAlgorithm<K, VV, EV> implements GraphAlgorithm<K, VV, EV,
DataSet<Vertex<K, Tuple2<Double, Double>>>> {
+
+ private int maxIterations;
+
+ /**
+ * Creates an instance of HITS algorithm.
+ *
+ * @param maxIterations the maximum number of iterations
+ */
+ public HITSAlgorithm(int maxIterations) {
+ Preconditions.checkArgument(maxIterations > 0, "The number of
maximum iteration should be greater than 0.");
+ this.maxIterations = maxIterations * 2 + 1;
+ }
+
+ @Override
+ public DataSet<Vertex<K, Tuple2<Double, Double>>> run(Graph<K, VV, EV>
netGraph) throws Exception {
+
+ ScatterGatherConfiguration parameter = new
ScatterGatherConfiguration();
+ parameter.setDirection(EdgeDirection.ALL);
+ parameter.registerAggregator("sumVertexValue", new
DoubleSumAggregator());
+
+ return netGraph
+ .mapVertices(new VertexInitMapper<K, VV>())
+ .mapEdges(new NullValueEdgeMapper<K, EV>())
+ .runScatterGatherIteration(new
VertexUpdate<K>(maxIterations),
+ new MessageUpdate<K,
NullValue>(maxIterations), maxIterations, parameter)
+ .getVertices();
+ }
+
+ /**
+ * Function that updates the value of a vertex by summing up the partial
+ * values from all messages and normalize the value.
+ */
+ @SuppressWarnings("serial")
+ public static final class VertexUpdate<K> extends
VertexUpdateFunction<K, Tuple2<Double, Double>, Double> {
+ private int maxIteration;
+ private DoubleSumAggregator doubleSumAggregator;
+
+ public VertexUpdate(int maxIteration) {
+ this.maxIteration = maxIteration;
+ }
+
+ @Override
+ public void preSuperstep() {
+ doubleSumAggregator =
getIterationAggregator("sumVertexValue");
+ }
+
+ @Override
+ public void updateVertex(Vertex<K, Tuple2<Double, Double>>
vertex, MessageIterator<Double> inMessages) {
+ double updateValue = 0;
+
+ for (double element : inMessages) {
+ if (getSuperstepNumber() == maxIteration) {
+ updateValue = element;
+ break;
+ }
+ updateValue += element;
+ }
+
+ // in the first iteration, no aggregation to call, init
sum with value of vertex
+ double iterationValueSum = 1.0;
+
+ if (getSuperstepNumber() > 1) {
+ iterationValueSum = Math.sqrt(((DoubleValue)
getPreviousIterationAggregate("sumVertexValue")).getValue());
+ }
+ if (getSuperstepNumber() != maxIteration) {
+ if (getSuperstepNumber() % 2 == 1) {
+ setNewVertexValue(new Tuple2<Double,
Double>(vertex.getValue().f0 / iterationValueSum, updateValue));
+
doubleSumAggregator.aggregate(Math.pow(updateValue, 2));
+ } else {
+ setNewVertexValue(new Tuple2<Double,
Double>(updateValue, vertex.getValue().f1 / iterationValueSum));
+
doubleSumAggregator.aggregate(Math.pow(updateValue, 2));
+ }
+ } else {
+
+ //final iteration to normalize hub score
+ setNewVertexValue(new Tuple2<Double,
Double>(vertex.getValue().f0 / iterationValueSum, vertex.getValue().f1));
+ }
+ }
+ }
+
+ /**
+ * Distributes the value of a vertex among all neighbor vertices and
sum all the
+ * value in every superstep.
+ */
+ @SuppressWarnings("serial")
+ public static final class MessageUpdate<K, EV> extends
MessagingFunction<K, Tuple2<Double, Double>, Double, EV> {
+ private int maxIteration;
+
+ public MessageUpdate(int maxIteration) {
+ this.maxIteration = maxIteration;
+ }
+
+ @Override
+ public void sendMessages(Vertex<K, Tuple2<Double, Double>>
vertex) {
+
+ // in the first iteration, no aggregation to call, init
sum with value of vertex
+ double iterationValueSum = 1.0;
+
+ if (getSuperstepNumber() > 1) {
+ iterationValueSum = Math.sqrt(((DoubleValue)
getPreviousIterationAggregate("sumVertexValue")).getValue());
+ }
+ for (Edge<K, EV> edge : getEdges()) {
+ K messageSource = getSuperstepNumber() % 2 == 1
? edge.getSource() : edge.getTarget();
+ K messageTarget = getSuperstepNumber() % 2 == 1
? edge.getTarget() : edge.getSource();
+ Double messageValue = getSuperstepNumber() % 2
== 1 ? vertex.getValue().f0 : vertex.getValue().f1;
+
+ if (!messageTarget.equals(vertex.getId())) {
+ if (getSuperstepNumber() !=
maxIteration) {
+ sendMessageTo(messageTarget,
messageValue / iterationValueSum);
+
+ // in order to make every
vertex updated
+ sendMessageTo(messageSource,
0.0);
+ } else {
+ sendMessageTo(messageSource,
iterationValueSum);
+ }
+ }
+ }
+ }
+ }
+
+ public static class VertexInitMapper<K, VV> implements
MapFunction<Vertex<K, VV>, Tuple2<Double, Double>> {
+
+ private static final long serialVersionUID = 1L;
+
+ public Tuple2<Double, Double> map(Vertex<K, VV> value) {
+
+ //init hub and authority value of each vertex
+ return new Tuple2<Double, Double>(1.0, 1.0);
--- End diff --
Fixed.
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