def log_term_frequency(document, term)
      count = document.term_count(term)
      if count > 0
        1 + log(count)
      else
        0
      end
    end
def log_term_frequency(document, term)
      count = document.term_count(term)
      if count > 0
        1 + log(count)
      else
        0
      end
    end
@see https://github.com/louismullie/treat/blob/master/lib/treat/workers/extractors/tf_idf/native.rb#L12

 SMART l, Chisholm LOGA