code: def pdf(self, f, y, Y_metadata=None):
          
          if isinstance(self.gp_link, link_functions.Identity):
              return self.pdf_link(f, y, Y_metadata=Y_metadata)
          else:
              inv_link_f = self.gp_link.transf(f)
              return self.pdf_link(inv_link_f, y, Y_metadata=Y_metadata)
docs: Evaluates the link function link(f) then computes the likelihood (pdf) using it
  
          .. math:
              p(y|\\lambda(f))
  
          :param f: latent variables f
          :type f: Nx1 array
          :param y: data
          :type y: Nx1 array
          :param Y_metadata: Y_metadata which is not used in student t distribution - not used
          :returns: likelihood evaluated for this point
          :rtype: float