message: replace Set with SetRow for better performance
diff: @@ -2092,11 +2092,7 @@ SparseMatrix* FiniteElementSpace::DerefinementMatrix(int old_ndofs,
  if (is_dg || !mark[m])
  {
  lR.GetRow(i, row);
  -
  - for (int j = 0; j < old_vdofs.Size(); j++)
  - {
  - R->Set(r, old_vdofs[j], row[j]);
  - }
  + R->SetRow(r, old_vdofs, row);
  mark[m] = 1;
  num_marked++;
  