Dear deal.II users,
I'd like to ask a question concerning the use of RHS function
represented by a DoF vector from another solver.
I'm trying to build RHS of one solver (A) using solution obtained with
another solver (B) , i.e. instead of Function there is a DoF vector.
Both solvers have the same coarse Triangulation (but differently
refined), but with different finite element systems: RHS source (solver
B) uses FESystem(FE_DGQ<dim>, 1, FESystem(FE_DGQ<dim>, dim), 1), the
solver A uses FESystem(FE_Q<dim>, 1, FE_Nedelec<dim>, 1). I have
devised the following scheme:
1. Solver A contains two DoFHandlers: one for RHS vector
(dof_handler_rhs), and another for the equation to solve
(dof_handler);
2. The solver B's output gets interpolated via
VectorTools::interpolate_to_different_mesh using dof_handler_rhs
as the destination space;
3. During solver A's assembly phase a separate FEValues is created
for RHS vector which is initialized to the same cell as the
FEValues corresponding to the equation;
4. FEValues::get_function_values gives RHS function values at the
quadrature points.
The problem here is the step 3: somehow I need to specify the same
geometric cell for two FEValues with different finite element
systems while preserving the ability to use get_function_values.
Surprisingly, there doesn't seem to be any obvious way to convert
CellAccessor given by Triangulation::active_cell_iterators() to
TriaIterator<DoFCellAccessor> needed for a "full reinit".
Of course, one can use VectorTools::point_value (or FEFieldFunction)
directly without interpolating, but it seems that the performance would
be very low: because of differing finite element systems, I cannot even
pass a cell hint. There is also an option to interpolate the B's
solution to the FE system used to solve A, but there might be an RHS
incompatible with FE_Nedelec elements.
Which tools could be used to overcome this problem? Or is my approach
deficient in general?
Best regards,
Alexander Kiselyov
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