message: Adding comment to explain usage of AbsMult.
diff: @@ -627,6 +627,9 @@ void BilinearForm::AssembleDiagonal(Vector &diag) const
  MFEM_ASSERT(diag.Size() == fes->GetTrueVSize(),
  "Vector for holding diagonal has wrong size!");
  const Operator *P = fes->GetProlongationMatrix();
  + // For an AMR mesh, a convergent diagonal is assembled with
  + // |P^T| d_e, where |P^T| has the entry-wise absolute values
  + // of the conforming prolongation transpose operator.
  if (P && !fes->Conforming())
  {
  Vector local_diag(P->Height());
  