Yeah, Roy is right, better to use quadrature. The approach I suggested initially would require you to project the exact solution into the FE space first, but you probably want to avoid that since it introduces a projection error into your calculation.
David On Tue, Jan 19, 2016 at 6:20 PM, Roy Stogner <royst...@ices.utexas.edu> wrote: > > This may not be what you want to do, IMHO. > > In the extreme case: If you compute the Uexact vector and then do the > vec*mat*vec, then you'll get a result of 0 for problems where your > method gives you an interpolant of the exact solution, even if that > interpolant doesn't equal the exact solution. > > If you evaluate the energy norm quadrature point by quadrature point, > you'll get a more accurate estimate of the error in general and you > can easily test for quadrature error by bumping up the order of your > rule. > --- > Roy > > > On Tue, 19 Jan 2016, David Knezevic wrote: > > Assemble the Uexact vector, then compute the difference e = U - Uexact. >> >> You can also refer to error_estimation/exact_solution.h, but I believe >> that's used for computing L2 or H1 error, not an arbitrary energy norm. >> >> David >> >> >> >> On Tue, Jan 19, 2016 at 5:04 PM, Junchao Zhang <junchao.zh...@gmail.com> >> wrote: >> >> How to get e = U - Uex? Is there a libmesh interface for that? >>> >>> --Junchao Zhang >>> >>> On Tue, Jan 19, 2016 at 3:57 PM, David Knezevic < >>> david.kneze...@akselos.com> wrote: >>> >>> Assuming you've already assembled K, so you can just do a matvec >>>> (SparseMatrix::vector_mult) followed by a dot product >>>> (NumericVector::dot). >>>> >>>> David >>>> >>>> >>>> >>>> On Tue, Jan 19, 2016 at 4:53 PM, Junchao Zhang <junchao.zh...@gmail.com >>>> > >>>> wrote: >>>> >>>> Hello, >>>>> I want to compute e^TKe as a measure of the error of a solution. Here >>>>> e = >>>>> U - Uex, supposing I know the analytic answer to the PDE. >>>>> How can I do it in libmesh? Is there an example? >>>>> Thank you. >>>>> >>>>> --Junchao Zhang >>>>> >>>>> >>>>> ------------------------------------------------------------------------------ >>>>> Site24x7 APM Insight: Get Deep Visibility into Application Performance >>>>> APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month >>>>> Monitor end-to-end web transactions and take corrective actions now >>>>> Troubleshoot faster and improve end-user experience. Signup Now! >>>>> http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 >>>>> _______________________________________________ >>>>> Libmesh-users mailing list >>>>> Libmesh-users@lists.sourceforge.net >>>>> https://lists.sourceforge.net/lists/listinfo/libmesh-users >>>>> >>>>> >>>> >>>> >>> >> ------------------------------------------------------------------------------ >> Site24x7 APM Insight: Get Deep Visibility into Application Performance >> APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month >> Monitor end-to-end web transactions and take corrective actions now >> Troubleshoot faster and improve end-user experience. Signup Now! >> http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 >> _______________________________________________ >> Libmesh-users mailing list >> Libmesh-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/libmesh-users >> >> >> ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Libmesh-users mailing list Libmesh-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-users
