code: def rsdl_rn(self, AX, Y):
          
  
          if not hasattr(self, '_cnst_nrm_c'):
              self._cnst_nrm_c = np.sqrt(np.linalg.norm(self.cnst_c0())**2 +
                                         np.linalg.norm(self.cnst_c1())**2)
          return max((np.linalg.norm(AX), np.linalg.norm(Y), self._cnst_nrm_c))
docs: Compute primal residual normalisation term.
  
          Overriding this method is required if methods :meth:`cnst_A`,
          :meth:`cnst_AT`, :meth:`cnst_B`, and :meth:`cnst_c` are not
          overridden.