/*

  * 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.giraph.benchmark;

 import org.apache.giraph.graph.BasicComputation;

 import org.apache.giraph.graph.Vertex;

 import org.apache.hadoop.io.FloatWritable;

 import org.apache.hadoop.io.IntWritable;

 import org.apache.hadoop.io.NullWritable;

 import java.io.IOException;

 /**

  * Implementation of PageRank in which vertex ids are ints, page rank values

  * are floats, and graph is unweighted.

  */

 public class PageRankComputation extends BasicComputation<IntWritable,

     FloatWritable, NullWritable, FloatWritable> {

   /** Number of supersteps */

   public static final String SUPERSTEP_COUNT =

       "giraph.pageRank.superstepCount";

   @Override

   public void compute(

       Vertex<IntWritable, FloatWritable, NullWritable> vertex,

       Iterable<FloatWritable> messages) throws IOException {

     if (getSuperstep() >= 1) {

       float sum = 0;

       for (FloatWritable message : messages) {

         sum += message.get();

       }

       vertex.getValue().set((0.15f / getTotalNumVertices()) + 0.85f * sum);

     }

     if (getSuperstep() < getConf().getInt(SUPERSTEP_COUNT, 0)) {

       sendMessageToAllEdges(vertex,

           new FloatWritable(vertex.getValue().get() / vertex.getNumEdges()));

     } else {

       vertex.voteToHalt();

     }

   }

 }