Dear Martin and Wolfgang,
" You seem to be looking for FEPointEvaluation. That class is shown in
step-19 and provides, for simple FiniteElement types, a much faster way to
evaluate solutions at arbitrary points within a cell. Do you want to give
it a try? "
I implemented the FEPointEvaluation approach like this:
FEPointEvaluation<1,1> fe_eval(mapping,
FE_Q<1>(1),
update_gradients | update_values);
fe_eval.reinit(cell,
make_array_view(std::vector<Point<1>>{ref_point_energy_vol}));
Vector<double> p_dofs(2);
cell->get_dof_values(solution_global, p_dofs);
fe_eval.evaluate(make_array_view(p_dofs),
EvaluationFlags::values |
EvaluationFlags::gradients);
double val = fe_eval.get_value(0);
Tensor<1,1> grad = fe_eval.get_gradient(0);
I am using FE_Q elements of degree one and a MappingQ object also of degree
one.
Frankly, I do not really understand the measured computation times.
My program has several loadsteps with nested Newton iterations:
Loadstep 1:
Assembly 1: cpu time 12.8 sec wall time 268.7 sec
Assembly 2: cpu time 17.7 sec wall time 275.2 sec
Assembly 3: cpu time 22.3 sec wall time 272.6 sec
Assembly 4: cpu time 23.8 sec wall time 271.3sec
Loadstep 2:
Assembly 1: cpu time 14.3 sec wall time 260.0 sec
Assembly 2: cpu time 16.9 sec wall time 262.1 sec
Assembly 3: cpu time 18.5 sec wall time 270.6 sec
Assembly 4: cpu time 17.1 sec wall time 262.2 sec
...
Using FEValues instead of FEPointEvaluation, the results are:
Loadstep 1:
Assembly 1: cpu time 23.9 sec wall time 171.0 sec
Assembly 2: cpu time 32.5 sec wall time 168.9 sec
Assembly 3: cpu time 33.2 sec wall time 168.0 sec
Assembly 4: cpu time 32.7 sec wall time 166.9 sec
Loadstep 2:
Assembly 1: cpu time 24.9 sec wall time 168.0 sec
Assembly 2: cpu time 34.7 sec wall time 167.3 sec
Assembly 3: cpu time 33.9 sec wall time 167.8 sec
Assembly 4: cpu time 34.3 sec wall time 167.7 sec
...
Clearly, the fluctuations using FEValues are smaller than in case of
FEPointEvaluation.
Anyway, using FEPointEvaluation the cpu time is smaller but the wall time
substantially bigger.
If I am not mistaken, the values cpu time 34.3 sec and wall time 167.7 sec
mean that
the cpu needs 34.3 sec to execute my assembly routine and has to wait in the
remaining 167.7-34.3 seconds.
This huge gap between cpu and wall time has to be related to what I do with
FEValues or FEPointEvaluation
as cpu and wall time are nearly balanced if I use either neither of them.
What might be the problem?
Best
Simon
Am Mi., 19. Okt. 2022 um 22:34 Uhr schrieb Wolfgang Bangerth <
bange...@colostate.edu>:
> On 10/19/22 08:45, Simon Wiesheier wrote:
> >
> > What I want to do boils down to the following:
> > Given the reference co-ordinates of a point 'p', along with the cell on
> > which 'p' lives,
> > give me the value and gradient of a finite element function evaluated at
> > 'p'.
> >
> > My idea was to create a quadrature object with 'p' being the only
> > quadrature point and pass this
> > quadrature object to the FEValues object and finally do the
> > .reinit(cell) call (then, of course, get_function_values()...)
> > 'p' is different for all (2.5 million) quadrature points, which is why I
> > create the FEValues object so many times.
>
> It's worth pointing out that is exactly what VectorTools::point_values()
> does.
>
> (As others have already mentioned, if you want to do that many many
> times over, this is too expensive and you should be using
> FEPointEvaluation instead.)
>
> Best
> W.
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth email: bange...@colostate.edu
> www: http://www.math.colostate.edu/~bangerth/
>
> --
> The deal.II project is located at http://www.dealii.org/
> For mailing list/forum options, see
> https://groups.google.com/d/forum/dealii?hl=en
> ---
> You received this message because you are subscribed to the Google Groups
> "deal.II User Group" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to dealii+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/dealii/cd1c8fa0-443d-b7bf-b433-f5ab033a247c%40colostate.edu
> .
>
--
The deal.II project is located at http://www.dealii.org/
For mailing list/forum options, see
https://groups.google.com/d/forum/dealii?hl=en
---
You received this message because you are subscribed to the Google Groups
"deal.II User Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to dealii+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/dealii/CAM50jEscu%2BSVwwUd6izNn9F9F1483QR%3DfFiBFbar27ZORDpeqA%40mail.gmail.com.
