ページランクのRuby実装

pagerank.rb

require "matrix"

class Graph
  D = 0.85
  EPS = 1 * 10 ** -5

  def initialize(matrix)
    @dimension = matrix.row_size

    elements = []
    @dimension.times do |i|
      elements[i] = []
      row_total = matrix.row(i).inject(&:+)
      @dimension.times do |j|
        elements[i][j] = row_total.zero? ? 0 : matrix[i, j].to_f / row_total
      end
    end
    @matrix = Matrix.rows(elements).transpose
    @vector = Matrix[[].fill(1.0 / @dimension, 0, @dimension)]
  end

  def pageranks
    loop do
      elements = []
      @dimension.times do |i|
        total = 0
        @dimension.times do |j|
          total += @matrix[i, j] * @vector[0, j]
        end
        elements[i] = D * total + (1.0 - D) / @dimension
      end
      new_vector = Matrix[elements]

      diff = 0
      @dimension.times do |i|
        diff += (new_vector[0, i] - @vector[0, i]).abs
      end

      return new_vector if diff < EPS
      @vector = new_vector
    end
  end
end

matrix = Matrix[[0, 1, 1, 0],
                [0, 0, 1, 0],
                [0, 1, 0, 0],
                [0, 1, 0, 0]]
graph = Graph.new(matrix)
p graph.pageranks