[Users] Accuracy issue of multipole moment calculations in QuasiLocalMeasures

[Ian Hinder]

On 24 Jun 2015, at 03:15, Hee Il Kim <heeilkim at gmail.com> wrote:

> Hi,
> 
> Recently, I found the multipole moment calculations in QuasiLocalMeasures show large errors, e.g. 20% for the second mass moment of my project. 
> 
> The error exists even in the test data of the thorn but it's around a few percent.

Note that the "test" directory contains regression tests, which are designed to check that the results haven't changed unintentionally when the code changes.  They are not meant to test correctness. As such, there is no claim of accuracy for their results.  In fact, they should be as small and fast as possible, which usually means that they are NOT accurate.  I'm not saying that there is no problem; just that the parameter files in the "test" directory should not be considered as tests of the correctness of the code.

> But it couldn't be improved even with increased resolution. From a rough investigation, I found this is because the one in coordinate construction which was supposed to be equal to cos(theta) for a stationary black hole deviates a bit, making erroneous value. I didn't go further. I'd like to know your opinion or any experiences on this. 
> 
> Cheers,
> 
> Hee Il
> p.s. I haven't checked whether there's an update of the thorn in the latest version of ET.

Which version of the code are you using?

It has not changed much recently.

$ svn log https://svn.cct.lsu.edu/repos/numrel/LSUThorns/QuasiLocalMeasures/trunk/

------------------------------------------------------------------------
r57 | eschnett | 2015-04-27 19:05:14 +0200 (Mon, 27 Apr 2015) | 1 line

Handle different CCTK_INT kinds
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r53 | eschnett | 2014-10-23 18:41:40 +0200 (Thu, 23 Oct 2014) | 1 line

Use IOUtil parameter for out_group_separator
------------------------------------------------------------------------
r52 | eschnett | 2014-10-23 17:41:45 +0200 (Thu, 23 Oct 2014) | 1 line

Use hyphen as group name separator
------------------------------------------------------------------------
r51 | eschnett | 2014-10-23 16:58:55 +0200 (Thu, 23 Oct 2014) | 1 line

Use hyphen as group name separator
------------------------------------------------------------------------
r50 | eschnett | 2014-10-23 16:40:31 +0200 (Thu, 23 Oct 2014) | 1 line

Use hyphen as group name separator
------------------------------------------------------------------------
r47 | rhaas | 2014-04-18 06:26:51 +0200 (Fri, 18 Apr 2014) | 2 lines

remove commented out code, remove unused variable

------------------------------------------------------------------------
r40 | diener | 2012-10-24 22:04:25 +0200 (Wed, 24 Oct 2012) | 5 lines

An EinsteinExact version of qlm-ks.par. Generates NaN's inside the
horizon, but those get's masked by the carpet mask and so does
not affect the norms. Passes the test when compared with the
data produced by qlm-ks.par (at least on my laptop).


-- 
Ian Hinder
http://members.aei.mpg.de/ianhin

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