[ET Trac] #2633: SummationByPart's Diff_gv aliased function does ont document which part of the grid the computed derivative is valid

[Peter Diener]

#2633: SummationByPart's Diff_gv aliased function does ont document which part of the grid the computed derivative is valid

 Reporter: Roland Haas
   Status: new
Milestone: 
  Version: 
     Type: bug
 Priority: minor
Component: 

Comment (by Peter Diener):

I suggest adding the following to the end of section 3.4:

In both cases, the derivatives are not calculated in ghost zones of  
inter-processor or symmetry boundaries, i.e. the returned derivatives are  
undefined in ghost zones and will require synchronization of either the  
derivatives or the evolved fields depending on the scheme used.

It would be wrong to switch to use one sided derivatives in ghost zones as,  
for most operators, the region, where one sided derivatives would be  
calculated, is larger than the ghost region. Hence some cells where centered  
finite differences could be calculated would contain one sided derivatives and  
the result would depend on the number of processors used.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2633/summationbyparts-diff_gv-aliased-function
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