Thank you for your quick response Dr. Bangerth! The context I would like to use du/dt in does not have a test function. So I guess I have to stick with the 2nd order elements or use the finite differencing in time (Thank you for the suggestion! I have not thought about that).
Best Johanna On Friday, December 8, 2023 at 6:50:42 PM UTC+1 Wolfgang Bangerth wrote: > On 12/8/23 10:40, Johanna Meier wrote: > > > > Is there a way to compute the actual numeric value of dudt.png at the > > quadrature points given the solution vector u? My first idea was to use > > quadratic elements and then just use FEValues.get_function_hessians() > with the > > solution u, which seems to work. I was wondering if it is also somehow > > possible to use linear elements. For example, when multiplying by a test > > function w and doing integration by parts on the right hand side to > shift one > > derivative to the test function. Would there be a way to evaluate this > new > > expression to get dudt.png? Or would this then give me w_dudt.png? > > To do this, you need to tell us what you need du/dt for, i.e., in which > context it appears. If that context has a test function, then yes of > course > you can integrate by parts. But if you want to output the time derivative > as a > pointwise value, you don't have a test function. > > Generally, I think you're probably going to be better off approximating > du/dt > based on the current and previous time steps, using some kind of finite > differencing in time. > > Best > W. > > -- > ------------------------------------------------------------------------ > Wolfgang Bangerth email: [email protected] > 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/9f385749-0bd6-4d68-9d30-a902c80cf5c6n%40googlegroups.com.
