code: def obfn_reg(self):
          r
  
          rl21 = np.sum(self.wl21 * np.sqrt(np.sum(self.obfn_gvar()**2,
                                                   axis=self.cri.axisC)))
          rgr = sl.rfl2norm2(np.sqrt(self.GHGf*np.conj(fvf)*fvf), self.cri.Nv,
                             self.cri.axisN)/2.0
          return (self.lmbda*rl21 + self.mu*rgr, rl21, rgr)
docs: r"""Compute regularisation terms and contribution to objective
          function. Regularisation terms are :math:`\| Y \|_1` and
          :math:`\| Y \|_{2,1}`.