[Users] Add a lapse condition

[Miguel Zilhão]

hi Erik,

in the LeanBSSNMoL thorn, the lapse gauge condition is implemented (together with all other 
right-hand-side evaluations) in the file calc_bssn_rhs.F90: 
https://bitbucket.org/canuda/lean_public/src/master/LeanBSSNMoL/src/calc_bssn_rhs.F90

the right-hand-side of the lapse function is done in line 1899:

  ! rhs_alph
    rhs_alph = rhs_alph - 2 * alph * trk

so adding another gauge condition should be a matter of changing this line to whatever you want.
let me know if this helps!

cheers,
Miguel

On 24/10/19 16:43, Erik Rodrígo Jiménez Vázquez wrote:
> Thank you!
> 
> Of course, any help would be greatly appreciated. What I need to change in the code of the 
> LeanBSSNMoL thorn?
> 
> Erik
> 
> 
> On Thu, Oct 24, 2019, 10:34 Miguel Zilhão <miguel.zilhao.nogueira at tecnico.ulisboa.pt 
> <mailto:miguel.zilhao.nogueira at tecnico.ulisboa.pt>> wrote:
> 
>     hi Erik,
> 
>     you can also try with the LeanBSSNMoL thorn, which is not Kranc-generated. adding another gauge
>     condition should be fairly simple; i can point you exactly to what you'd need to change in the code
>     if you need.
> 
>     cheers,
>     Miguel
> 
>     On 24/10/19 16:21, Peter Diener wrote:
>      > Hi Erik,
>      >
>      > McLachlan is a thorn generated from a tool named Kranc from high level tensorial expressions in
>      > Mathematica. So if you have
>      > access to Mathematica you can add additional lapse conditions in the
>      > mathematica source file located in:
>      >
>      > arrangements/McLachlan/m/McLachlan_BSSN.m
>      >
>      > and then regenerate the McLachlan thorn using
>      >
>      > make McLachlan_BSSN.out
>      >
>      > in the arrangements/McLachlan/m directory.
>      >
>      > I admit the section on gauge conditions is rather messy as the selection of particular gauges
>     are
>      > done based on conditionals on thorn parameters, but hopefully you can figure this out.
>     Otherwise let
>      > me know and I'll be happy to help.
>      >
>      > Cheers,
>      >
>      >    Peter
>      >
>      > On Thursday 2019-10-24 00:14, Erik Rodrígo Jiménez Vázquez wrote:
>      >
>      >> Date: Thu, 24 Oct 2019 00:14:05
>      >> From: Erik Rodrígo Jiménez Vázquez <erjive at ciencias.unam.mx <mailto:erjive at ciencias.unam.mx>>
>      >> To: users at einsteintoolkit.org <mailto:users at einsteintoolkit.org>
>      >> Subject: [Users] Add a lapse condition
>      >>
>      >> Dear all
>      >>
>      >> Is there a way to add different gauge conditions for the lapse? I'm trying
>      >> to add a gauge shock avoid lapse for the Bona-Masso family of slicing
>      >> conditions
>      >>
>      >> dot alpha = -alpha^2 f(alpha) K
>      >>
>      >> with f(alpha)=1+constant/alpha^2
>      >>
>      >> I don't know if I should add a thorn that complements the McLachlan thorn,
>      >> or what is the correct procedure to implement the gauge condition?
>      >> Furthermore, this kind of gauge condition allows to the lapse become
>      >> negative which I know is a serious drawback when the lapse collapses to
>      >> zero, however I want to do some numerical experiments with this kind of
>      >> lapse.
>      >>
>      >> Any help is very welcome. Thanks
>      >> Erik
>      >>
>      >>
>      >>
>      >
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