code: def ledoit_wolf(self):
          
          X = np.nan_to_num(self.X.values)
          shrunk_cov, self.delta = covariance.ledoit_wolf(X)
          return self.format_and_annualise(shrunk_cov)
docs: Calculate the Ledoit-Wolf shrinkage estimate.
  
          :return: shrunk sample covariance matrix
          :rtype: np.ndarray