[ET Trac] [Einstein Toolkit] #1398: make evolution_method etc. parameters of ADMBase steerable

[Einstein Toolkit]

#1398: make evolution_method etc. parameters of ADMBase steerable
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  Reporter:  rhaas                  |       Owner:                     
      Type:  enhancement            |      Status:  review             
  Priority:  minor                  |   Milestone:                     
 Component:  EinsteinToolkit thorn  |     Version:  development version
Resolution:                         |    Keywords:  ADMBase            
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Comment (by rhaas):

 Switching evolution system requires extra care and is potentially very
 dangerous (mostly though one just gets poison when not using it
 correctly), yes. One needs to schedule the equivalent of ADM_to_BSSN in
 Post_Recover_Variables - on all timelevels - which is currently disabled
 with a page long comment (by me...) explaining why running
 Post_Recover_Variables on all timelevels is detrimental to bitwise exact
 recovery. These are "you-asked-for-it/famous-last-words" kind of options.
 Use at your own risk.

 I have to admit I am not sure I see why this necessarily conflicts with a
 desire for bitwise identical recovery. Here the user is telling the system
 that she wants something different from what was used in the previous
 checkpoint so must expect changes.

 Using the file reader is currently not a very convenient alternative since
 it cannot currently automatically recover the grid structure from the data
 files and one is forced to construct a set of input parameters to eg
 CarpetRegrid2 that mimic the settings (set via the grid scalars of
 CarpetRegrid2) that were active at the time the checkpoint files were
 written.

 There is not much experience yet on how well this method will work. So
 let's wait for a bit to see how feasible it turns out to be. If it is
 fraught with difficulties it might be faster to extent the file reader to
 somehow recover the grid structure from files and use that. In that case
 it would be nice to be able to set the initial cctk_iteration value as
 well (agreed, no one should depend on cctk_iteration since it is just a
 counter and does not necessarily have a simple relationship with
 cctk_time, many thorns do though).

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1398#comment:3>
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