def populate_markov_sum
    @markov_weighted_sum = {}
    @markov_chains.each do |word,followers|
      @markov_weighted_sum[word] = followers.inject(0) {|sum,kv| sum + kv[1]}
    end
  end
def populate_markov_sum
    @markov_weighted_sum = {}
    @markov_chains.each do |word,followers|
      @markov_weighted_sum[word] = followers.inject(0) {|sum,kv| sum + kv[1]}
    end
  end
populate the weight-sums for each chain
 (an optimization)