[Users] No Meeting tomorrow, Monday May 15th

Ian Hinder ian.hinder at aei.mpg.de
Tue May 17 10:26:25 CDT 2011

On 17 May 2011, at 16:39, Peter Diener wrote:

> Hi,
> For the distorted rotating black hole case I thought I had the runs 
> completed. However, when I took a look at the waveforms, I saw only 2nd 
> order convergence (very nice 2nd order convergence, though). I had 
> unfortunately not noticed that the default values for WeylScal4::fd_order 
> and Multipole::integration_method resulted in only 2nd order accurate wave 
> extraction. I'm currently rerunning with modified parameter settings.
> Is there any reason why the default values for those parameters could not 
> be set to give higher accuracy?

It seemed that the simplest and lowest order of accuracy made a sensible default, and would work with any number of ghost zones.  I agree that it is a little surprising for someone who always works with higher order methods, but then SummationByParts also defaults to second order, presumably for the same reasons.

For WeylScal4, this would require a larger number of ghost zones than 1.  Kranc (unfortunately) does not check that you are using a sufficient number of ghost-zones for the finite difference method in use, so this could lead to hard-to-detect problems for new users.  I will see how easy it is to add this check in (https://github.com/ianhinder/Kranc/issues/29).  

For Multipole, I am unsure as to the effects of using higher order integration on BBH waveforms.  I tested that the integration methods are correct and converge at the required order for test functions, but high order methods often lead to high frequency errors if the data is not smooth, so out of an abundance of caution, I always use the low order method with a very high resolution angular grid (this is not very expensive in a production simulation).

> Cheers,
>   Peter
> On Sun, 15 May 2011, Frank Loeffler wrote:
>> Hi,
>> At least Tanja, Roland, myself and Erik cannot join the ET call
>> tomorrow, so let's cancel the meeting for this week.
>> However: in order not to lose focus in the ET paper it would be nice to
>> have some progress report for the largest missing sections, e.g., the
>> examples, on this mailing list.
>> For the TOVs:
>> I ran a couple of resolutions of a standard TOV model and can easily see
>> the fundamental mode. It is pretty clear that in order to get a good
>> measurement of the frequency the resolution cannot be laptop or
>> workstation-friendly, but that is to be expected. I cannot easily see or
>> measure any overtones though - it's a nice, damped sine. I will finish
>> to run the high-res simulations and then include that frequency
>> measurement in the paper, comparing with the expected result.
>> Frank
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Ian Hinder
ian.hinder at aei.mpg.de

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