Exp(grad_scope, Div(grad_scope, Square(grad_scope, op.output(0)), two)));
  grad_outputs->push_back(dx);
  return grad_scope.status();
}
REGISTER_GRADIENT_OP("Ndtri", NdtriGrad);

Status LgammaGrad(const Scope& scope, const Operation& op,
                  const std::vector<Output>& grad_inputs,
                  std::vector<Output>* grad_outputs) {
  auto grad = grad_inputs[0];