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.
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Wolfgang Bangerth email: [email protected]
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