[Users] looking for help with CT_MultiLevel

Slinker, Kyle Patrick kslink at live.unc.edu
Wed Jun 22 09:42:25 CDT 2016

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.

Kyle Slinker
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