[ET Trac] [Einstein Toolkit] #963: Improve McLachlan accuracy

Einstein Toolkit trac-noreply at einsteintoolkit.org
Wed Jun 20 15:41:55 CDT 2012


#963: Improve McLachlan accuracy
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 Reporter:  eschnett               |       Owner:     
     Type:  enhancement            |      Status:  new
 Priority:  major                  |   Milestone:     
Component:  EinsteinToolkit thorn  |     Version:     
 Keywords:                         |  
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 James van Meter provided me with an optimised version of McLachlan. He
 states:

 1. You are not taking full advantage of the chi=exp(-2phi) variable.
 There are several terms you divide by chi or chi^2 in expressions with
 overall factors exp(-4phi).  I rewrote the BSSN equations to make these
 cancellations before coding.  So where you have an expression of the form
 chi^2(A+B/chi^2), I have chi^2A+B.  This gives a slight but noticeable
 advantage in both accuracy and performance.

 2. I added Hamiltonian-constraint-damping terms due to Duez et al.  These
 terms don't seem to be well-known but they are effective.

 3. I added a Gamma-constraint-damping term due to Yo et al.

 4. I enforce det(g)=1.

 I have not tested this new version yet, but James suggests to include it
 into the Einstein Toolkit.

-- 
Ticket URL: <https://trac.einsteintoolkit.org/ticket/963>
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