[Users] looking for help with CT_MultiLevel

Eloisa Bentivegna eloisa.bentivegna at ct.infn.it
Wed Jun 22 14:41:22 CDT 2016

On 22/06/16 16:42, Slinker, Kyle Patrick wrote:
> I have been working with CT_MultiLevel in an attempt to solve the
> non-conformally-flat constraint equations and I'm wondering if there is
> an error in the thorn. Where I'm potentially seeing an issue is in
> CT_SolvePsiEquation.cc and CT_SolveErrorEquation.cc in the definitions
> of dtime (for both files this is line 33 in the Brahe release).
> First of all, having 0.5 in this definition means that the coefficient
> for the central point in the finite difference is hard-coded to a second
> order stencil. When using fourth order, this coefficient should be 0.4,
> I believe. This effectively changes the SOR omega.
> More importantly, I don't think it accounts for ct_cxx, ct_cyy, or
> ct_czz. So the central point in the finite difference is not getting
> multiplied by whatever coefficient the user is setting.
> Am I misunderstanding how the thorn works or are these really problems?
> I've attached what I believe is a way to fix them. Thanks for your help.

Dear Kyle,

thanks for the comments. I am not sure I understand your points though:
in CT_MultiLevel, fd_order is used to control the approximation order of
spatial derivatives, while dtime appears in the way the "time"
derivative is discretized. These two are in principle independent.

Can you clarify which derivative you believe is wrong?


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