[ET Trac] [Einstein Toolkit] #1797: allow new timelevels to be created at runtime

[Einstein Toolkit]

#1797: allow new timelevels to be created at runtime
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  Reporter:  rhaas        |       Owner:                     
      Type:  enhancement  |      Status:  review             
  Priority:  optional     |   Milestone:                     
 Component:  Cactus       |     Version:  development version
Resolution:               |    Keywords:  Cactus Carpet PUGH 
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Comment (by rhaas):

 Replying to [comment:5 hinder]:
 > So timelevel cycling would then have the effect of copying tl_N into
 tl_{N+1}, and leaving tl0 as it is, so that it is identical to tl1?  This
 sounds like a good idea to me.  If we can then omit MoL's copy, I think we
 can then use MoL with only a single timelevel with, e.g. RK4, which is all
 it should need.

 Avoiding the copying does not avoid multiple timelevels since MoL uses
 tl=0 as scratch space during the computation. Eg the final
 LinearCombination for RK4 is:

   y_0_new = 1.0 * y_0_from_last_RK_step + scratchVar - 4/3 * y_1

 What Erik proposes does not change anything from the point of the MoL time
 intergrator, it just moves MoL's Initialcopy from the beginning of EVOL
 (when MoL's group runs) to just before CCTK_PRESTEP (when Carpet cycles
 timelevels).

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1797#comment:7>
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