code: def first_fit(self, train_x, train_y):
          
          train_x, train_y = np.array(train_x), np.array(train_y)
  
          self._x = np.copy(train_x)
          self._y = np.copy(train_y)
  
          self._distance_matrix = edit_distance_matrix(self._x)
          k_matrix = bourgain_embedding_matrix(self._distance_matrix)
          k_matrix[np.diag_indices_from(k_matrix)] += self.alpha
  
          self._l_matrix = cholesky(k_matrix, lower=True)  # Line 2
  
          self._alpha_vector = cho_solve((self._l_matrix, True), self._y)  # Line 3
  
          self._first_fitted = True
          return self
docs: Fit the regressor for the first time.