" What type of Mapping are you using? If you take a look at https://github.com/dealii/dealii/blob/ad13824e599601ee170cb2fd1c7c3099d3d5b0f7/source/matrix_free/fe_point_evaluation.cc#L40-L95 you can see when the fast path of FEPointEvaluation is taken. Indeed, the slow path is (FEValues). One question: are you running in release or debug mode? "
I use FE_Q<1>(1) with a MappingQ<1>(1) and FE_Q<2>(1) with a MappingQ<2>(1). I am running in release mode. Best, Simon Am Do., 20. Okt. 2022 um 16:53 Uhr schrieb Peter Munch < peterrmue...@gmail.com>: > > FEPointEvaluation creates an FEValues object along with a quadrature > object under the hood. > Closer inspection revealed that all constructors, destructors,... > associated with FEPointEvaluation > need roughly 5000 instructions more (per call!). > That said, FEValues is indeed the faster approach, at least for FE_Q > elements. > > What type of Mapping are you using? If you take a look at > https://github.com/dealii/dealii/blob/ad13824e599601ee170cb2fd1c7c3099d3d5b0f7/source/matrix_free/fe_point_evaluation.cc#L40-L95 > you can see when the fast path of FEPointEvaluation is taken. Indeed, the > slow path is (FEValues). One question: are you running in release or debug > mode? > > Hope this brings us closer to the issue, > Peter > > On Thursday, 20 October 2022 at 16:47:17 UTC+2 Simon wrote: > >> Update: >> >> I profiled my program with valgrind --tool=callgrind and could figure out >> that >> FEPointEvaluation creates an FEValues object along with a quadrature >> object under the hood. >> Closer inspection revealed that all constructors, destructors,... >> associated with FEPointEvaluation >> need roughly 5000 instructions more (per call!). >> That said, FEValues is indeed the faster approach, at least for FE_Q >> elements. >> >> export DEAL_II_NUM_THREADS=1 >> eliminated the gap between cpu and wall time. >> Using FEValues directly, I get cpu time 19.8 seconds >> and in the case of FEPointEvaluation cpu time = 21.9 seconds; >> Wall times are in the same ballpark. >> Out of curiosity, why produces multi-threading such high wall times (200 >> seconds) in my case?. >> >> These times are far too big given that the solution of the linear system >> takes only about 13 seconds. >> But based on what all of you have said, there is probably no other to way >> to implement my problem. >> >> Best >> Simon >> >> Am Do., 20. Okt. 2022 um 11:55 Uhr schrieb Simon Wiesheier < >> simon.w...@gmail.com>: >> >>> 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 < >>> bang...@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: bang...@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+un...@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/cb9c0d1a-77f5-4920-86dc-bc38ee6ab1dfn%40googlegroups.com > <https://groups.google.com/d/msgid/dealii/cb9c0d1a-77f5-4920-86dc-bc38ee6ab1dfn%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- 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. 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