[ET Trac] [Einstein Toolkit] #1627: Merge rewrite branch of McLachlan

[Einstein Toolkit]

#1627: Merge rewrite branch of McLachlan
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  Reporter:  eschnett               |       Owner:                     
      Type:  enhancement            |      Status:  new                
  Priority:  major                  |   Milestone:                     
 Component:  EinsteinToolkit thorn  |     Version:  development version
Resolution:                         |    Keywords:                     
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Comment (by eschnett):

 Merged.

 Answers to Ian's questions:

 - Performance benchmark results were posted to the mailing list. The
 upshot is that performance remains largely the same, except for
 McLachlan's built-in dissipation that is now much faster, probably
 slightly faster than thorn Dissipation.
 - Turning off dissipation: Yes, this is still a Kranc-time choice; this is
 necessary for performance. This the new performance is as good as or
 better than thorn Dissipation, I think this is now a non-issue.
 - Advection terms: The current code is not slowed down by the advection
 terms. I expect that other restructuring led to the same speed improvement
 that we gained from splitting out the advection terms previously.

 - {{{ML_}}} prefix: I've kept this for backward compatibility.
 - FromBSSNCalc calculates everything that can be calculated from the BSSN
 state vector. This is not just the RHS, it also includes constraints, ADM
 variables, etc. Maybe "EverythingFromBSSNCalc" would be a good name. This
 change would be invisible to the user.
 - Renaming "phiW" to "cf": If so, then this needs to be done NOW. Please
 open a discussion on the mailing list.
 - Changing parameter names: I'd like to not do this for backward
 compatibility. Many parameter names don't change, and changing all of them
 is more disruptive than changing just a few gauge-related ones.
 - The helper thorn could be avoided. This seemed an orthogonal change, so
 I've omitted it for the time begin. We can look at it in a week or two, in
 case there's an unexpected problem with the rewrite.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1627#comment:4>
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