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<p><b style="font-size: 11pt; font-family: Calibri, sans-serif;">From:</b><span style="font-size: 11pt; font-family: Calibri, sans-serif;"> Roland Haas <rhaas@illinois.edu></span><br>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>Sent:</b> Tuesday, March 3, 2020 6:29 PM<br>
<b>To:</b> Hamilton, Maria<br>
<b>Cc:</b> Peter Diener<br>
<b>Subject:</b> Re: Questions about the nsnstohmns.par</font>
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<div class="PlainText">Hello Maria,<br>
<br>
> 1. The parameter has refinement levels, and regrid radius, but<br>
> does not have time_refinement_factors. Is this on purpose? Should it<br>
> be there?<br>
Without setting time_refinement_factors it uses the default which is a<br>
factor of 2 between each level. Many of the BBH parfiles use a factor<br>
of 1 between the coarsest level, however for NS this is often not<br>
required (the differing factor is only there to cure an instability in<br>
the shift condition).<br>
<br>
> 2. CarpetRegrid2 is given 3 num_centers, if first and second are<br>
> the NSs, what is the role of the third, why does it have only 1<br>
> num_level, and why is not centered at 0?<br>
The third one is created without any boxes. I will contain the<br>
merged star / black hole once it forms. The Triger thorn (see your<br>
question 4) is used to enable refinement levels for this center once a<br>
horizon is about to form (lapse drops below a given value). Since it is<br>
only a placeholder initially it is set to 1 level and since it will<br>
capture the black hole that forms at the origin it is centered on the<br>
origin.<br>
<br>
> 3. CarpetRegrid2 is given position_x_1 and position_x_2, if those<br>
> are the centers for the NSs, why is 15.1875 for a 45 radius? If I<br>
> want the radius to be 50, how do I change this?<br>
45 is in km. So 45km is ~30Msun distance which gives a radius of<br>
~15Msun (Msun being the code unit as well).<br>
<br>
> 4. Why do I need Trigger?<br>
Trigger is needed to enable grid changes once a horizon is about to<br>
form.<br>
<br>
> 5. If I want to search for a BH as final result, how do I add<br>
> AHFinderDirect?<br>
Isn't it already there? If not then you can add it as usual but set eg<br>
the parameter "find_individual_after[n]" of the horizon to some huge<br>
value (1e6 or so) and have the Trigger thorn steer that value to "0."<br>
once it enables the central grid patch so that the horizonfinder starts<br>
looking for horizons (there may also be a more direct "enable"<br>
parameter listed in AHFinderDirect's param.ccl that you could use<br>
instead of hacking find_invidual_after, or whatever its name actually<br>
is.<br>
<br>
> 6. SphericalSurface is given 5 surface, but surface [2] is<br>
> skipped. Why?<br>
That one was likely intended / used for a black hole horizon. There is<br>
no reason for the set of used surfaces being contiguous really.<br>
<br>
> Thank you for your time, and I hope you won't mind my questions.<br>
No worries. As usual I would like to encourage these question to be<br>
asked on the users mailing list so that others can contribute (and<br>
benefit from the answers eventually).<br>
<br>
Yours,<br>
Roland<br>
<br>
-- <br>
My email is as private as my paper mail. I therefore support encrypting<br>
and signing email messages. Get my PGP key from <a href="http://pgp.mit.edu" id="LPlnk24305" previewremoved="true">
http://pgp.mit.edu</a> .<br>
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