docs: def _quadratic_sum_cost(self, state: _STATE) -> float:
          """Cost function that sums squares of lengths of sequences.
  
          Args:
            state: Search state, not mutated.
  
          Returns:
            Cost which is minus the normalized quadratic sum of each linear
            sequence section in the state. This promotes single, long linear
            sequence solutions and converges to number -1. The solution with a
            lowest cost consists of every node being a single sequence and is
            always less than 0.
          """
          cost = 0.0
          total_len = float(len(self._c))
          seqs, _ = state
          for seq in seqs:
              cost += (len(seq) / total_len) ** 2
          return -cost