code: def ystep(self):
          r
  
          AXU = self.AX + self.U
          Y0 = (self.rho*(self.block_sep0(AXU) - self.S)) / (self.W**2 +
                                                             self.rho)
          Y1 = self.Pcn(self.block_sep1(AXU))
          self.Y = self.block_cat(Y0, Y1)
docs: r"""Minimise Augmented Lagrangian with respect to
          :math:`\mathbf{y}`.