/*

  * 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.MutableVertex;

 import org.apache.hadoop.io.DoubleWritable;

 import org.apache.hadoop.io.LongWritable;

 /**

  * Shared computation of class Pregel-style PageRank computation for benchmark

  * classes.

  */

 public class PageRankComputation {

   /** Number of supersteps */

   public static final String SUPERSTEP_COUNT =

       "PageRankBenchmark.superstepCount";

   /**

    * Do not construct.

    */

   private PageRankComputation() { }

   /**

    * Generic page rank algorithm.

    *

    * @param vertex Vertex to compute on.

    * @param messages Iterator of messages from previous superstep.

    */

   public static void computePageRank(

       MutableVertex<LongWritable, DoubleWritable, DoubleWritable,

       DoubleWritable> vertex, Iterable<DoubleWritable> messages) {

     if (vertex.getSuperstep() >= 1) {

       double sum = 0;

       for (DoubleWritable message : messages) {

         sum += message.get();

       }

       DoubleWritable vertexValue = new DoubleWritable(

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

       vertex.setValue(vertexValue);

     }

     if (vertex.getSuperstep() < vertex.getConf().getInt(SUPERSTEP_COUNT, -1)) {

       long edges = vertex.getNumEdges();

       vertex.sendMessageToAllEdges(

           new DoubleWritable(vertex.getValue().get() / edges));

     } else {

       vertex.voteToHalt();

     }

   }

 }