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PageRankComputation xref
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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  package org.apache.giraph.benchmark;
20  
21  import org.apache.giraph.graph.BasicComputation;
22  import org.apache.giraph.graph.Vertex;
23  import org.apache.hadoop.io.FloatWritable;
24  import org.apache.hadoop.io.IntWritable;
25  import org.apache.hadoop.io.NullWritable;
26  
27  import java.io.IOException;
28  
29  /**
30   * Implementation of PageRank in which vertex ids are ints, page rank values
31   * are floats, and graph is unweighted.
32   */
33  public class PageRankComputation extends BasicComputation<IntWritable,
34      FloatWritable, NullWritable, FloatWritable> {
35    /** Number of supersteps */
36    public static final String SUPERSTEP_COUNT =
37        "giraph.pageRank.superstepCount";
38  
39    @Override
40    public void compute(
41        Vertex<IntWritable, FloatWritable, NullWritable> vertex,
42        Iterable<FloatWritable> messages) throws IOException {
43      if (getSuperstep() >= 1) {
44        float sum = 0;
45        for (FloatWritable message : messages) {
46          sum += message.get();
47        }
48        vertex.getValue().set((0.15f / getTotalNumVertices()) + 0.85f * sum);
49      }
50  
51      if (getSuperstep() < getConf().getInt(SUPERSTEP_COUNT, 0)) {
52        sendMessageToAllEdges(vertex,
53            new FloatWritable(vertex.getValue().get() / vertex.getNumEdges()));
54      } else {
55        vertex.voteToHalt();
56      }
57    }
58  }