Hello,
when is setting the parameter
CarpetReduce::min_max_time_interpolation = no
recommended?
Cheers, Luca
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- Log ----------------------------------------------------------------- commit 10d085aa3043a139cc56fb0538bfe4e4741becd9 Author: Erik Schnetter schnetter@gmail.com Date: Mon Mar 18 16:25:22 2013 -0400
CarpetReduce: New parameter min_max_time_interpolation
New parameter min_max_time_interpolation to disable time interpolation for min and max reductions.
commit afc9bb25ad65041be3705053da280be415f5ca9d Author: Erik Schnetter schnetter@gmail.com Date: Mon Mar 18 15:16:56 2013 -0400
CarpetReduce: Don't require a valid cctkGH unless really needed
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Summary of changes: Carpet/CarpetReduce/param.ccl | 4 ++++ Carpet/CarpetReduce/src/reduce.cc | 20 ++++++++------------ 2 files changed, 12 insertions(+), 12 deletions(-)
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On Nov 16, 2013, at 2:12 , Luca Baiotti baiotti@ile.osaka-u.ac.jp wrote:
Hello,
when is setting the parameter
CarpetReduce::min_max_time_interpolation = no
recommended?
Luca
Carpet offers reduction operators that span the whole grid hierarchy, i.e. that take the whole computational domain into account. If you request such a reduction (e.g. average, L2-norm, or maximum) at a time in between two coarse grid steps, then Carpet interpolates these coarse grid data to that time. Generally, this is what one wants.
However, this time interpolation can produce data that never actually existed. Let us consider a grid point that is hit by a shock. At an earlier time, the density may be 0.1, and at a later time, the density may be 1.0. Time interpolation does not use a limiter, and can thus produce an interpolated density that is either larger than 1.0 or that is less than 0.1, or even negative.
Note that these interpolated data are most likely only used for output, and that you asked for data at a time where the code never produced data (in between coarse grid steps). Thus such wrong density values are less critical than they may seem at first.
The new parameter "CarpetReduce::min_max_time_interpolation = no" avoids time interpolation in this case. Instead, the most current data are used. This is also not correct, but at least avoids the over- or under-shooting that may otherwise be present.
A more correct solution to this issue would be to use a different time interpolation algorithm for hydrodynamics variables that switches to a lower-order time interpolation in this case.
-erik
users@lists.einsteintoolkit.org
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Erik Schnetter -
Luca Baiotti