Hi Peter,
Thanks so much! I asked because I'd like to try running simulations with the modified shift condition described in this paper (second page): https://arxiv.org/abs/gr-qc/0511103
Some terms that feature in the usual gamma driver equations are dropped, and the lapse appears in the time derivative of beta. Would I have to make changes to the Kranc code in order to implement such a condition?
Best,
Gwyneth
On Wed, Dec 28, 2016 at 10:57 AM, Peter Diener diener@cct.lsu.edu wrote:
Hi Gwyneth,
The parameters to control the gamma driver shift condition is something that we would like to make more transparent. I have to go and look at the Kranc code, in order to figure out how things work.
When ShiftBCoeff = 1 and ShiftAdvectionCoeff = 1 (both are the default values) we are evolving the gamma driver shift that is listed on the wiki you point to.
ShiftGammaCoeff should be set to 0.75 (it's the 3/4 in the equation for the shift). It's unfortunate that 0.75 is not the default value for ShiftGammaCoeff, as this is the only value that is ever used (as far as I know). BetaDriver is the eta value in the eqaution for B. ShiftAlphaPower is a leftover parameter from before the moving puncture approach came into use and currently has no effect in the code.
Let me know if you have any other questions.
Cheers,
Peter
On Tuesday 2016-12-27 10:31, Gwyneth Allwright wrote:
Date: Tue, 27 Dec 2016 10:31:55
From: Gwyneth Allwright allgwy001@myuct.ac.za To: users@einsteintoolkit.org Subject: [Users] McLachlan Shift Condition
Hi All,
I'm new to the Einstein Toolkit and would like to double check what the ML_BSSN parameters ShiftGammaCoeff, BetaDriver and ShiftAlphaPower refer to. I tried looking in the param.ccl file, but it still wasn't 100% clear to me.
As far as I understand, the shift condition used by McLachlan is the gamma driver, given here: http://grwiki.physics.ncsu.edu/wiki/Shift_Conditions. What value of eta does ML_BSSN use?
Thanks,
Gwyneth
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