code: def _swap_rows(self, i, j):
          
  
          L = np.eye(3, dtype='intc')
          L[i, i] = 0
          L[j, j] = 0
          L[i, j] = 1
          L[j, i] = 1
          self._L.append(L.copy())
          self._A = np.dot(L, self._A)
docs: Swap i and j rows
  
          As the side effect, determinant flips.