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[Garth Wells <question97361@xxxxxxxxxxxxxxxxxxxxx>]

Question #97361 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/97361

    Status: Open => Answered

Garth Wells proposed the following answer:

Patrick Riesen wrote:
> New question #97361 on DOLFIN: 
> https://answers.launchpad.net/dolfin/+question/97361
> 
> hi, i want to change some values of a subfunction of a mixed function
> with iterating over the dofs this mixed function (_uw). However, the
> mixed function has two subspaces which are identical.
> 
> if i want to go over the dofs of _uw[1] as
> 
> for(CellIterator cell(_fluid->mesh()); !cell.end(); ++cell) {
> 
> ufc_cell.update(*cell);
> 
> _uw->restrict(w_coeffs.get(), w_sub->element(), *cell, ufc_cell, -1);
> 
> 
> _uw->function_space().dofmap().tabulate_dofs(cell_dofs.get(),
> ufc_cell, cell->index());
> 
> _uw->vector().get(w_coeffs.get(), 
> w_sub->dofmap().local_dimension(ufc_cell), cell_dofs.get());
> 
> for(dolfin::uint i = 0; i < cell_dims; i++) w_coeffs[i] = w_coeffs[i]
> * scV_init;
> 
> _uw->vector().set(w_coeffs.get(), 
> w_sub->dofmap().local_dimension(ufc_cell), cell_dofs.get()); }
> 
> i thought this will change the values of _uw[1], but it will change
> the values of _uw[0], although i specified the second sub-element
> w_sub. So it should modify the values in _uw->vector() which
> correspond to _uw[1]. Does somebody see what i am doing wrong, or is
> this maybe not as supposed to be?
>

I can't follow the example code very easily, but it sounds like you're
missing the dof map offset (see _ufc_offset inside DofMap).

Can you make a simpler example without restrict, and vetors, etc? Just
try getting the (sub) dof map and see which entries it points to.

Garth

> many thanks for the help, patrick
> 
> 
>

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