[Users] Einstein Toolkit Meeting Minutes

[Frank Loeffler]

Hi

Present were: Bhavesh, Elo, Erik, Frank, Gwyneth, Ian H., Peter, Roberto, Steven, and Vassili

Status on KNLs
 Some independently developed optionlists exist, but none are production-ready:
 - Erik's optionlist on Cori: in branch in simfactory2
 - Frank will put his option list into simfactory.
 - Eloisa has one for Marconi + KNL, and will also put it in simfactory.
 
Test suites and Jenkins:
 - Erik: optimizations on "jenkins" use optimization, performance difference ~8%
   - discussion about
    - whether to use optimizations or not / whether 8% are ok to loose
    - whether optimizations "dangerous" or not.
   - result for now: try to see if testsuites are broken and fix, if possible.
 - Eloisa will look at boostedpuncture test case
 - Roland will look at Spec test suites
 - Frank &| Roland will have a look at the hydro failure

Piraha CST parsing (Stev):
 - caching parse-tree cuts down time practically to 0
 - files holding cache (one per ccl file) will be within configurations
 - plan: new ticket, branch, eventually inclusion
 - parallelism problematic with Perl, but may not be needed anyway

Gwyneth asked:
 - Constraints: what/how to use to calculate?
   - ML_AMD_Contstraints: uses ADM constraints, independent of evolution 
     system
   - McLachlan: uses BSSN variables, no need to calculate ADM variables
   result: It does (and should) not really matter.
     Preferences for one or the other exist, and may depend on
     particular simulation specifics, but both should get the results
     to within numerical accuracy.
 - What thorn to use for which output type (basic/scalar/ascii)
   (Frank: It would probably be good to have this as overview on a page or so.)
 - Question about comment in bbh gallery example par file:
   "SummationByParts::sbp_upwind_deriv": not required for that parameter file
     would drop order of derivatives near boundary in some cases, but
     derivatives are not used here
 - ADMMass: how to measure
   - using initial data output (but that might differ from the one on the finite comp. grid)
   - ADMMass thorn: surface integral    or
   - ADMMass thorn: volume integral (but needs thorn not in the toolkit to excise BHs) or
   - QuasiLocalMeasures: surface integral
 - time refinement factors on coarse grids
   - Stricter requirements on time step on very coarse grids than regular cfl factor may
     lead to instabilities (gauge evolution in particular).
   - Result: don't need to use if no instability seen.

Frank

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