/*

  * 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.edge.Edge;

 import org.apache.giraph.edge.MutableEdge;

 import org.apache.giraph.graph.Vertex;

 import org.apache.hadoop.io.DoubleWritable;

 import org.apache.hadoop.io.LongWritable;

 import java.io.IOException;

 /**

  * Implementation of Page Rank algorithm on a weighted graph.

  */

 public class WeightedPageRankComputation extends BasicComputation<LongWritable,

     DoubleWritable, DoubleWritable, DoubleWritable> {

   /** Number of supersteps */

   public static final String SUPERSTEP_COUNT =

       "giraph.weightedPageRank.superstepCount";

   @Override

   public void compute(

       Vertex<LongWritable, DoubleWritable, DoubleWritable> vertex,

       Iterable<DoubleWritable> messages) throws IOException {

     if (getSuperstep() == 0) {

       // Normalize out edge weights

       double outEdgeSum = 0;

       for (Edge<LongWritable, DoubleWritable> edge : vertex.getEdges()) {

         outEdgeSum += edge.getValue().get();

       }

       for (MutableEdge<LongWritable, DoubleWritable> edge :

           vertex.getMutableEdges()) {

         edge.setValue(new DoubleWritable(edge.getValue().get() / outEdgeSum));

       }

     } else {

       double messageSum = 0;

       for (DoubleWritable message : messages) {

         messageSum += message.get();

       }

       vertex.getValue().set(

           (0.15f / getTotalNumVertices()) + 0.85f * messageSum);

     }

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

       for (Edge<LongWritable, DoubleWritable> edge : vertex.getEdges()) {

         sendMessage(edge.getTargetVertexId(),

             new DoubleWritable(

                 vertex.getValue().get() * edge.getValue().get()));

       }

     } else {

       vertex.voteToHalt();

     }

   }

 }