On 7 Mar 2019, at 07:40, Antoni Ramos Buades
<[email protected]<mailto:[email protected]>> wrote:
Hi,
Roland you are right it is forming and destroying a common box each time the
outburst of noise happens. Do you know how one could get rid of this noise, or
if there are some parameters of Carpet which one could add to the parameter
file to avoid such a behaviour?
Hi Antoni,
There is this parameter in CarpetRegrid2:
CCTK_REAL min_fraction "Minimum fraction of required refined points that need
to be present in a refined region" STEERABLE=always
{
0:* :: ""
} 0.9
When two boxes overlap, CarpetRegrid2 has to make a decision about whether to
use the union of the two boxes, or to replace the two boxes with a single
enclosing box. This code is in
carpet/CarpetRegrid2/src/property.cc<http://property.cc> in the function
combine_regions::test_impl. The decision is made based on the number of point
in the union of the two boxes, vs the number of points in a single enclosing
box. It will leave the regions separate if
min_fraction * combined_size > regions_size
which, with the default of 0.9, means that the number of points in the single
enclosing region is greater than 1.11 times the number of points in the
original regions. The logic for this is that having lots of regions means lots
of faces, edges and corners, and more communication and prolongation, which can
affect performance and might also be undesirable due to creating numerical
error features such as reflections. On the other hand, the single enclosing
region will contain more points, and hence will be more expensive to evolve.
min_fraction allows you to decide how many extra points you are willing to
evolve, for the sake of having only a single box. If there would be more than
1/min_fraction times the number of points by combining, the code does not
combine.
If you set
CarpetRegrid2::min_fraction = 1
then Carpet will never create a single enclosing box, but will always give you
a box based on the union of the points in the two boxes.
Ninja'd by Roland. Sigh...
--
Ian Hinder
Research Software Engineer
University of Manchester, UK
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