message: Set direction=0 if pseudo_gradient=0 (OWL-QN)
diff: @@ -425,7 +425,10 @@ where
  let d = if let Some(l1_coeff) = self.l1_coeff {
  line_problem.with_l1_constraint(l1_coeff, &param, &prev_grad);
  let zeros = r.zero_like();
  - P::max(&r.mul(&prev_grad).signum(), &zeros)
  + P::max(
  + &r.mul(&prev_grad).sub(&F::min_positive_value()).signum(),
  + &zeros,
  + )
  .mul(&r)
  .mul(&float!(-1.0))
  } else {
  