# File lib/bundler/similarity_detector.rb, line 30
    def levenshtein_distance(this, that, ins=2, del=2, sub=1)
      # ins, del, sub are weighted costs
      return nil if this.nil?
      return nil if that.nil?
      dm = []        # distance matrix

      # Initialize first row values
      dm[0] = (0..this.length).collect { |i| i * ins }
      fill = [0] * (this.length - 1)

      # Initialize first column values
      for i in 1..that.length
        dm[i] = [i * del, fill.flatten]
      end

      # populate matrix
      for i in 1..that.length
        for j in 1..this.length
          # critical comparison
          dm[i][j] = [
               dm[i-1][j-1] +
                 (this[j-1] == that[i-1] ? 0 : sub),
                   dm[i][j-1] + ins,
               dm[i-1][j] + del
         ].min
        end
      end

      # The last value in matrix is the Levenshtein distance between the strings
      dm[that.length][this.length]
    end