code: def ystep(self):
          r
  
          self.Y = np.asarray(sp.prox_l2(
              self.AX + self.U, (self.lmbda/self.rho)*self.Wtvna,
              axis=self.saxes), dtype=self.dtype)
docs: r"""Minimise Augmented Lagrangian with respect to
          :math:`\mathbf{y}`.