Also: it can depend on integration error in the integration of the L2 Error. We're still using quadrature to integrate... so if that quadrature is poor you can "miss" solution features on a coarse grid that then show up as you refine the mesh (which refines the quadrature too) leading to higher error.
One way to combat that is to use the "extra quadrature order" capability when computing the L2 Norm of the error... it allows you to "fine up" your quadrature to give you a better integral on the coarse mesh. I don't remember exactly how to do that on the moment (currently on my phone on the subway)... so if you snoop around a bit and don't find it... write back in. Derek On Thu, Jan 28, 2016 at 1:36 PM Roy Stogner <royst...@ices.utexas.edu> wrote: > > On Wed, 27 Jan 2016, Junchao Zhang wrote: > > > Time = 0.025, refinement step = 0, elements = 10, l2_error = > 0.443873 > > Time = 0.025, refinement step = 1, elements = 40, l2_error = > 0.045196 > > Time = 0.025, refinement step = 2, elements = 160, l2_error = > 0.131169 > > Time = 0.025, refinement step = 3, elements = 640, l2_error = > 0.116789 > > Time = 0.025, refinement step = 4, elements = 2560, l2_error = > 0.118175 > > > > > > I am curious why sometimes L2 error gets bigger, e.g., from r_step 1 to > > r_step 2. Don't more refinements give smaller errors? > > If your solve's discretization error is your only source of error, and > if you're solving a self-adjoint problem, then more refinements should > *always* give you smaller errors. > > This problem isn't self-adjoint, so the convection term can cause > convergence to be more erratic, but I don't think that's the problem > here. > > The problem might be that you've got two sources of discretization > error here: the discretization for the solve, and the discretization > for the initial conditions. If you project the initial conditions and > then refine, rather than refine and then project, you won't actually > have improved your approximation of the initial conditions. So you > won't converge to the exact solution you want, you'll converge to the > solution of the PDE with the wrong initial conditions. > --- > Roy > > > ------------------------------------------------------------------------------ > 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
