code: def _distance_covariance_sqr_naive(x, y, exponent=1):
      
      a = _distance_matrix(x, exponent=exponent)
      b = _distance_matrix(y, exponent=exponent)
  
      return mean_product(a, b)
docs: Naive biased estimator for distance covariance.
  
      Computes the unbiased estimator for distance covariance between two
      matrices, using an :math:`O(N^2)` algorithm.