pg-twitter-distributed.gsql

use graph twitter 

drop query pagerank

CREATE DISTRIBUTED QUERY pagerank (int iteration, float dampingFactor)
FOR GRAPH twitter 
{
  # In each iteration, compute a score for each vertex:
  #   score = dampingFactor + (1-dampingFactor)* sum(received scores from its neighbors).
  # The pageRank algorithm stops after running iteration iterations
  # This implementation is based on https://graphsql.atlassian.net/wiki/display/UGH/Query+Example%3A+PageRank
  # To only measure the execution time, we do not print a large number of results. only the max difference is returned

  MaxAccum<float> @@maxDifference = 3.1415926;
  SumAccum<float> @received_score = 0; # sum of scores each vertex receives from neighbors
  SumAccum<float> @score = 1;   # initial score for every vertex is 1.
  
  AllV = {MyNode.*};   #  Start with all vertices of type Page
  WHILE TRUE LIMIT iteration DO
    #@@maxDifference = 0;
    AllV = SELECT s
         FROM AllV:s-(MyEdge)->:t
         ACCUM t.@received_score += s.@score/s.outdegree()
         POST-ACCUM t.@score = dampingFactor + (1-dampingFactor) * t.@received_score,
                    t.@received_score = 0;
                    #@@maxDifference +=   abs(t.@score - t.@score');
  END; # end while loop
  PRINT @@maxDifference;   # print the results
} # end query

install query pagerank