code: def inversion(origin=(0, 0, 0)):
          
          mat = -np.eye(4)
          mat[3, 3] = 1
          mat[0:3, 3] = 2 * np.array(origin)
          return SymmOp(mat)
docs: Inversion symmetry operation about axis.
  
          Args:
              origin (3x1 array): Origin of the inversion operation. Defaults
                  to [0, 0, 0].
  
          Returns:
              SymmOp representing an inversion operation about the origin.