MainIanRogers.scala

// http://www.cs.princeton.edu/~chazelle/courses/BIB/pagerank.htm
object MainIanRogers {

  case class Edge(src: Int, dest: Int)

  def main(args: Array[String]) {

    val edges = Seq(
      Edge(0, 1),
      Edge(0, 2),
      Edge(1, 2),
      Edge(2, 0),
      Edge(3, 2)
    )

    val vertices = 4

    val alpha = 0.85

    val pr = new Array[Double](vertices)
    val delta = new Array[Double](vertices)
    val deg = new Array[Double](vertices)

    // determine vertex degrees
    edges.map(edge => deg(edge.src) += 1)
    println("deg=" + deg.mkString(", "))

    for (i <- Range(0, 20)) {
      println("iteration " + (i + 1))

      // compute the delta
      for (vertex <- Range(0, vertices))
        delta(vertex) = 0
      edges.map(edge => delta(edge.dest) += alpha * pr(edge.src) / deg(edge.src))

      println("delta=" + delta.mkString(", "))

      // compute the new PR
      for (vertex <- Range(0, vertices)) {
        pr(vertex) = (1 - alpha) + delta(vertex)
      }

      println("pr=" + pr.mkString(", "))
      println()
    }

    println("pr=" + pr.mkString(", "))
  }

}