<div dir="ltr">Hi Peter,<br><br>Thanks! I had a look at the part of the code you pointed me to, and it does seem like a straightforward modification.<br><br>The rules for dotbeta[ua], dot[beta[ua]] and dot[B[ua]] make sense to me, besides for the sign of the first IfThen term in dot[B[ua]]:<br><br>dot[B[ua]] -> IfB[+ dotXt[ua]<br> <font color="#ff0000">+ IfThen[fixAdvectionTerms != 0,<br> Upwind[beta[ub], Xt[ua], lb],<br> 0]</font><br> - (betaDriverValue<br> (+ B[ua]<br> +<br> IfThen[fixAdvectionTerms != 0 && advectShift != 0,<br> Upwind[beta[ub], beta[ua], lb] /<br> (shiftGammaCoeffValue alpha^<br> shiftAlphaPower),<br> 0]))<br> + IfThen[fixAdvectionTerms == 0 && advectShift != 0,<br> Upwind[beta[ub], B[ua], lb],<br> 0]<br> + Dissipation[B[ua]],<br> 0]<br><br>Comparing with the gamma driver condition in the wiki (<a href="http://grwiki.physics.ncsu.edu/wiki/Shift_Conditions">http://grwiki.physics.ncsu.edu/wiki/Shift_Conditions</a>), shouldn't this term be negative, or am I missing something?<br><br>You mentioned that shiftAlphaPower doesn't affect the code any more, but it seems to feature in the rule for dotbeta[ua]. Wouldn't I be able to make the time derivative of beta proportional to alpha by setting the parameter shiftAlphaPower = 1?<br><br>Thanks again for your help, and Happy (soon-to-be) New Year!<br><br>Best,<br><br>Gwyneth
<div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Dec 30, 2016 at 12:04 PM, Peter Diener <span dir="ltr"><<a href="mailto:diener@cct.lsu.edu" target="_blank">diener@cct.lsu.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi Gwyneth,<br>
<br>
On Wednesday 2016-12-28 15:00, Gwyneth Allwright wrote:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Date: Wed, 28 Dec 2016 15:00:10<br>
From: Gwyneth Allwright <<a href="mailto:allgwy001@myuct.ac.za" target="_blank">allgwy001@myuct.ac.za</a>><br>
To: Peter Diener <<a href="mailto:diener@cct.lsu.edu" target="_blank">diener@cct.lsu.edu</a>><br>
Cc: <a href="mailto:users@einsteintoolkit.org" target="_blank">users@einsteintoolkit.org</a><br>
Subject: Re: [Users] McLachlan Shift Condition<span class=""><br>
<br>
Hi Peter,<br>
Thanks so much! I asked because I'd like to try running simulations with the<br>
modified shift condition described in this paper (second<br>
page): <a href="https://arxiv.org/abs/gr-qc/0511103" rel="noreferrer" target="_blank">https://arxiv.org/abs/gr-qc/05<wbr>11103</a><br>
<br>
Some terms that feature in the usual gamma driver equations are dropped, and<br>
the lapse appears in the time derivative of beta. Would I have to make<br>
changes to the Kranc code in order to implement such a condition?<br>
</span></blockquote>
<br>
There is presently no parameter choice that would implement that<br>
particular version of the gamma driver shift in McLachlan. So, yes<br>
modifying the code would be the only option. It should be<br>
straightforward to modify the Kranc script and then regenerate the code<br>
(if you have a Mathematica license).<br>
<br>
The Kranc script can be found in:<br>
<br>
Cactus/repos/mclachlan/m/McLac<wbr>hlan_BSSN.m<br>
<br>
You'll have to modify the relevant part (i.e. the rules for dot[beta[ua]]<br>
and dot[B[ua]]) of the calculation EverythingFromBSSNCalc.<br>
<br>
It's probably easier for you to simply replace those complicated rules<br>
by your version for testing instead of adding options to add it to the<br>
existing shift.<br>
<br>
If it turns out to be useful for you, we can then later think about how<br>
to add it to McLachlan permanently.<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Best,<br>
<br>
Gwyneth<br>
</blockquote>
<br>
Cheers,<br>
<br>
Peter<div class="HOEnZb"><div class="h5"><br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On Wed, Dec 28, 2016 at 10:57 AM, Peter Diener <<a href="mailto:diener@cct.lsu.edu" target="_blank">diener@cct.lsu.edu</a>> wrote:<br>
Hi Gwyneth,<br>
<br>
The parameters to control the gamma driver shift condition is<br>
something<br>
that we would like to make more transparent. I have to go and<br>
look at<br>
the Kranc code, in order to figure out how things work.<br>
<br>
When ShiftBCoeff = 1 and ShiftAdvectionCoeff = 1 (both are the<br>
default<br>
values) we are evolving the gamma driver shift that is listed on<br>
the<br>
wiki you point to.<br>
<br>
ShiftGammaCoeff should be set to 0.75 (it's the 3/4 in the<br>
equation for<br>
the shift). It's unfortunate that 0.75 is not the default value<br>
for<br>
ShiftGammaCoeff, as this is the only value that is ever used (as<br>
far as<br>
I know). BetaDriver is the eta value in the eqaution for B.<br>
ShiftAlphaPower is a leftover parameter from before the moving<br>
puncture<br>
approach came into use and currently has no effect in the code.<br>
<br>
Let me know if you have any other questions.<br>
<br>
Cheers,<br>
<br>
Peter<br>
<br>
On Tuesday 2016-12-27 10:31, Gwyneth Allwright wrote:<br>
<br>
Date: Tue, 27 Dec 2016 10:31:55<br>
From: Gwyneth Allwright <<a href="mailto:allgwy001@myuct.ac.za" target="_blank">allgwy001@myuct.ac.za</a>><br>
To: <a href="mailto:users@einsteintoolkit.org" target="_blank">users@einsteintoolkit.org</a><br>
Subject: [Users] McLachlan Shift Condition<br>
<br>
Hi All,<br>
<br>
I'm new to the Einstein Toolkit and would like to<br>
double check what the<br>
ML_BSSN parameters ShiftGammaCoeff, BetaDriver and<br>
ShiftAlphaPower refer to.<br>
I tried looking in the param.ccl file, but it still<br>
wasn't 100% clear to me.<br>
<br>
As far as I understand, the shift condition used by<br>
McLachlan is the gamma<br>
driver, given here:<br>
<a href="http://grwiki.physics.ncsu.edu/wiki/Shift_Conditions" rel="noreferrer" target="_blank">http://grwiki.physics.ncsu.ed<wbr>u/wiki/Shift_Conditions</a>.<br>
What value of eta does ML_BSSN use?<br>
<br>
Thanks,<br>
<br>
Gwyneth<br>
<br>
<br>
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