code: def Ey(self, f):
          r
          return np.exp(f) if self.tranfcn == 'exp' else softplus(f)
docs: r"""
          Expected value of the Poisson likelihood.
  
          Parameters
          ----------
          f: ndarray
              latent function from the GLM prior (:math:`\mathbf{f} =
              \boldsymbol\Phi \mathbf{w}`)
  
          Returns
          -------
          Ey: ndarray
              expected value of y, :math:`\mathbb{E}[\mathbf{y}|\mathbf{f}]`.