message: For testing purposes, copy the implementation of the method
  void FiniteElementSpace::RefinementOperator::Mult
  from the master branch, while keeping the new implementation in
  a commented out block.
diff: @@ -1100,6 +1100,59 @@ FiniteElementSpace::RefinementOperator::~RefinementOperator()
  delete old_elem_dof;
  }
  +// TODO: choose which version of this method we want to keep: the first one is
  +// the one from master and the second one below is the new implementation.
  +#if 1
  +void FiniteElementSpace::RefinementOperator
  +::Mult(const Vector &x, Vector &y) const
  +{
  + Mesh* mesh = fespace->GetMesh();
  + const CoarseFineTransformations &rtrans = mesh->GetRefinementTransforms();
  +
  + Array<int> dofs, old_dofs, old_vdofs;
  +
  + Array<char> processed(fespace->GetVSize());
  + processed = 0;
  +
  + int vdim = fespace->GetVDim();
  + int old_ndofs = width / vdim;
  +
  + for (int k = 0; k < mesh->GetNE(); k++)
  + {
  + const Embedding &emb = rtrans.embeddings[k];
  + const Geometry::Type geom = mesh->GetElementBaseGeometry(k);
  + const DenseMatrix &lP = localP[geom](emb.matrix);
  +
  + fespace->GetElementDofs(k, dofs);
  + old_elem_dof->GetRow(emb.parent, old_dofs);
  +
  + for (int vd = 0; vd < vdim; vd++)
  + {
  + old_dofs.Copy(old_vdofs);
  + fespace->DofsToVDofs(vd, old_vdofs, old_ndofs);
  +
  + for (int i = 0; i < dofs.Size(); i++)
  + {
  + double rsign, osign;
  + int r = fespace->DofToVDof(dofs[i], vd);
  + r = DecodeDof(r, rsign);
  +
  + if (!processed[r])
  + {
  + double value = 0.0;
  + for (int j = 0; j < old_vdofs.Size(); j++)
  + {
  + int o = DecodeDof(old_vdofs[j], osign);
  + value += x[o] * lP(i, j) * osign;
  + }
  + y[r] = value * rsign;
  + processed[r] = 1;
  + }
  + }
  + }
  + }
  +}
  +#else
  void FiniteElementSpace::RefinementOperator
  ::Mult(const Vector &x, Vector &y) const
  {
  @@ -1136,6 +1189,7 @@ void FiniteElementSpace::RefinementOperator
  }
  }
  }
  +#endif
  void FiniteElementSpace::RefinementOperator
  ::MultTranspose(const Vector &x, Vector &y) const
  