message: Add comment for transfer operator offsets array
diff: @@ -947,6 +947,11 @@ protected:
  const FiniteElementSpace &fes_ho;
  const FiniteElementSpace &fes_lor;
  + // The restriction and prolongation operators are represented as dense
  + // elementwise matrices (of potentially differing sizes, because of mixed
  + // meshes or p-refinement). The matrix entries are stored in the R and P
  + // arrays. The entries of the ith high-order element are stored at the
  + // index given by offsets[i].
  mutable Array<double> R, P;
  Array<int> offsets;
  