code: def transfer_matrix(self, superoperator):
          
          if not self.is_orthonormal():  # pragma no coverage
              raise ValueError("transfer_matrix() only implemented for orthonormal operator bases.")
          return self.basis_transform.H * superoperator.data * self.basis_transform
docs: Compute the transfer matrix :math:`R_{jk} = \tr[P_j sop(P_k)]`.
  
          :param qutip.Qobj superoperator: The superoperator to transform.
          :return: The transfer matrix in sparse form.
          :rtype: scipy.sparse.csr_matrix