# [Users] Refinement levels 3 to 5.

Bilal Hameed bilalhameedawan962 at gmail.com
Wed Aug 26 07:45:37 CDT 2020

```Awesome, thanks!

On Wed, Aug 26, 2020, 5:37 PM Roland Haas <rhaas at illinois.edu> wrote:

> Hello Bilal,
>
> > When I change, Carpet::max_refinement_levels = 5 (instead of 3). and
> > I also changed,
> >
> > CarpetRegrid2::num_centres  = 1
> > #CarpetRegrid2::num_levels_1 = 3
> > #CarpetRegrid2::radius_1[1]  = 1
> > #CarpetRegrid2::radius_1[2]  = 1
> >
> > CarpetRegrid2::num_levels_1 = 5
> > CarpetRegrid2::radius_1[1]  = 5
> > CarpetRegrid2::radius_1[2]  = 5
> > CarpetRegrid2::radius_1[3]  = 5
> > CarpetRegrid2::radius_1[4]  = 5
> You are correct in changing both Carpet::max_refinement_levels which
> controls the maximum possible number of refinement levels as well as
> CarpetRegrid2::num_levels_1 which controls that actual number of
> refinement levels used.
>
> > My simulation runs successfully. but fourth and fifth levels shown
> > only nan as follows,
> >
> > INFO (CT_MultiLevel): === Level 2 ===
> > INFO (CT_MultiLevel):  * Equation #0: 10 iterations, norm of final
> residual = 2.5741620337e-05
> > INFO (CT_MultiLevel):  * Equation #1: 10 iterations, norm of final
> residual = 8.7340004508e-06
> > INFO (CT_MultiLevel):  * Equation #2: 10 iterations, norm of final
> residual = 8.7156879010e-06
> > INFO (CT_MultiLevel):  * Equation #3: 10 iterations, norm of final
> residual = 8.6982806224e-06
> > INFO (CT_MultiLevel): === Level 3 ===
> > INFO (CT_MultiLevel):  * Equation #0: 1 iterations, norm of final
> residual = nan
> > INFO (CT_MultiLevel):  * Equation #1: 1 iterations, norm of final
> residual = nan
> > INFO (CT_MultiLevel):  * Equation #2: 1 iterations, norm of final
> residual = nan
> > INFO (CT_MultiLevel):  * Equation #3: 1 iterations, norm of final
> residual = nan
>
> > What else should I fix?
>
> I am not really familiar (at all, never having used it) with
> CT_MultiLevel itself. However looking at the parfile
> repos/ctthorns/CT_MultiLevel/par/constraints_spherical.par you can see
> that it sets:
>
> CT_MultiLevel::topMGlevel          = 2
>
> and that parameter is described in the thorn's documentation (in the
> doc directory or online)
>
> http://einsteintoolkit.org/thornguide/CTThorns/CT_MultiLevel/documentation.html
> as:
>
> --8<--
> The only other parameter which must be set to ensure correct operation
> is CT_MultiLevel::topMGlevel, which tells the solver which is the ﬁnest
> reﬁnement level that covers the entire domain in which the equation is
> to be solved. All levels below and including this will be used in the
> classical multigrid sense (e.g., in a V- or FMG-cycle). The ones above
> will be treated as local AMR boxes, and be solved via a multilevel
> prescription; presently, this involves simply interpolating the
> solution from the topMGlevel reﬁnement level at the end of the
> multigrid part and relaxing it progressively, from coarser to ﬁner, on
> all the local grids.
> --8<--
>
> so since you changed max_refinement_levels from 3 to 5 I would also
> change topMGlevel from 2 to 4.
>
> Yours,
> Roland
>
> --
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