code: def flip_one(self, tour):
          
          n_accepts = n_rejects = 0
          any_tag_ACCEPT = False
          for i, t in enumerate(tour):
              if i == 0:
                  score, = self.evaluate_tour_Q(tour)
              self.signs[t] = -self.signs[t]
              score_flipped, = self.evaluate_tour_Q(tour)
              if score_flipped > score:
                  n_accepts += 1
                  tag = ACCEPT
              else:
                  self.signs[t] = -self.signs[t]
                  n_rejects += 1
                  tag = REJECT
              self.flip_log("FLIPONE ({}/{})".format(i + 1, len(self.signs)),
                            score, score_flipped, tag)
              if tag == ACCEPT:
                  any_tag_ACCEPT = True
                  score = score_flipped
          logging.debug("FLIPONE: N_accepts={} N_rejects={}"
                        .format(n_accepts, n_rejects))
          return ACCEPT if any_tag_ACCEPT else REJECT
docs: Test flipping every single contig sequentially to see if score
          improves.