message: Simplify hessian in MaxEntropy test
diff: @@ -77,12 +77,10 @@ impl ArgminOp for MaxEntropy {
  let log_pdot = self.F.dot(&p.t());
  let log_z = log_pdot.mapv(|x| x.exp()).sum().ln();
  let y = (log_pdot - log_z).mapv(|x| x.exp());
  - // TODO: replace with Array2::from_diag if/when it is available
  + // TODO: replace with Array2::from_diag when it is available
  // ndarray#673
  let mut y2_diag = Array2::zeros((y.len(), y.len()));
  - for (idx, val) in y.iter().enumerate() {
  - y2_diag[[idx, idx]] = val.clone();
  - }
  + y2_diag.diag_mut().assign(&y);
  let tmp = self.F.clone() - self.F.clone().t().dot(&y);
  let hess = self.F.clone().t().dot(&y2_diag.dot(&tmp));
  Ok(hess)
  