I just tried both, neither of them make a difference. I got exactly the same curve with either combination.
Thanks! Wang weizhuo On Tue, Oct 16, 2018 at 8:06 PM Matthew Knepley <[email protected]> wrote: > On Tue, Oct 16, 2018 at 7:26 PM Weizhuo Wang <[email protected]> > wrote: > >> Hello again! >> >> After some tweaking the code is giving right answers now. However it >> start to disagree with MATLAB results ('traditional' way using matrix >> inverse) when the grid is larger than 100*100. My PhD advisor and I >> suspects that the default dimension of the Krylov subspace is 100 in the >> test case we are running. If so, is there a way to increase the size of the >> subspace? >> > > 1) The default subspace size is 30, not 100. You can increase the subspace > size using > > -ksp_gmres_restart n > > 2) The problem is likely your tolerance. The default solver tolerance is > 1e-5. You can change it using > > -ksp_rtol 1e-9 > > Thanks, > > Matt > > >> >> [image: Disagrees.png] >> >> Thanks! >> >> Wang Weizhuo >> >> On Tue, Oct 9, 2018 at 2:50 AM Mark Adams <[email protected]> wrote: >> >>> To reiterate what Matt is saying, you seem to have the exact solution on >>> a 10x10 grid. That makes no sense unless the solution can be represented >>> exactly by your FE space (eg, u(x,y) = x + y). >>> >>> On Mon, Oct 8, 2018 at 9:33 PM Matthew Knepley <[email protected]> >>> wrote: >>> >>>> On Mon, Oct 8, 2018 at 9:28 PM Weizhuo Wang <[email protected]> >>>> wrote: >>>> >>>>> The code is attached in case anyone wants to take a look, I will try >>>>> the high frequency scenario later. >>>>> >>>> >>>> That is not the error. It is superconvergence at the vertices. The real >>>> solution is trigonometric, so your >>>> linear interpolants or whatever you use is not going to get the right >>>> value in between mesh points. You >>>> need to do a real integral over the whole interval to get the L_2 error. >>>> >>>> Thanks, >>>> >>>> Matt >>>> >>>> >>>>> On Mon, Oct 8, 2018 at 7:58 PM Mark Adams <[email protected]> wrote: >>>>> >>>>>> >>>>>> >>>>>> On Mon, Oct 8, 2018 at 6:58 PM Weizhuo Wang <[email protected]> >>>>>> wrote: >>>>>> >>>>>>> The first plot is the norm with the flag -pc_type lu with respect to >>>>>>> number of grids in one axis (n), and the second plot is the norm without >>>>>>> the flag -pc_type lu. >>>>>>> >>>>>> >>>>>> So you are using the default PC w/o LU. The default is ILU. This will >>>>>> reduce high frequency effectively but is not effective on the low >>>>>> frequency >>>>>> error. Don't expect your algebraic error reduction to be at the same >>>>>> scale >>>>>> as the residual reduction (what KSP measures). >>>>>> >>>>>> >>>>>>> >>>>> >>>>> -- >>>>> Wang Weizhuo >>>>> >>>> >>>> >>>> -- >>>> What most experimenters take for granted before they begin their >>>> experiments is infinitely more interesting than any results to which their >>>> experiments lead. >>>> -- Norbert Wiener >>>> >>>> https://www.cse.buffalo.edu/~knepley/ >>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.cse.buffalo.edu_-7Eknepley_&d=DwMFaQ&c=OCIEmEwdEq_aNlsP4fF3gFqSN-E3mlr2t9JcDdfOZag&r=hsLktHsuxNfF6zyuWGCN8x-6ghPYxhx4cV62Hya47oo&m=EFM29ATgv4U8PjXEtfgMkuxKr5DGscMlH-j769W5W_4&s=grgSL2LaDCthvYvvFITmeOOWPCwgmNfYRPs94N8kmOs&e=> >>>> >>> >> >> -- >> Wang Weizhuo >> > > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > > https://www.cse.buffalo.edu/~knepley/ > <http://www.cse.buffalo.edu/~knepley/> > -- Wang Weizhuo
