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#2887: TwoPunctures does not support Slow-Start Lapse.
by Roland Haas 11 Sep '25

11 Sep '25

#2887: TwoPunctures does not support Slow-Start Lapse. Reporter: Zach Etienne Status: open Milestone: Version: Type: enhancement Priority: major Component: Comment (by Roland Haas): Please apply. -- Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2887/twopunctures-does…

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#2887: TwoPunctures does not support Slow-Start Lapse.
by Zach Etienne 11 Sep '25

11 Sep '25

#2887: TwoPunctures does not support Slow-Start Lapse. Reporter: Zach Etienne Status: open Milestone: Version: Type: enhancement Priority: major Component: Comment (by Zach Etienne): When Slow Start Lapse \(SSL\) is disabled, setting initial\_lapse = psi^n with n = -2 results in evolutions that are nearly indistinguishable from initial\_lapse = W. However, keeping the default as initial\_lapse = W is safer for future compatibility: if SSL is later enabled and the lapse is not initially W, you’ll see a spike in the Einstein constraints. Here’s why: SSL exponentially relaxes the lapse toward \*W\* very early in the wormhole-to-trumpet transition, smoothing the sharp outgoing-lapse feature that accounts for >99.9% of constraint violations in moving-puncture BBH evolutions \(see [https://arxiv.org/abs/2404.01137](https://arxiv.org/abs/2404.01137)\). If the lapse isn’t initially set to W, then “Slow Start” would be better termed “Fast and Reckless”, as the initial lapse will be exponentially driven to W from whatever it was set to initially – leading to the aforementioned _spike_ in Einstein constraints. -- Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2887/twopunctures-does…

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#2706: Update default TwoPunctures parameters, or at least default parameters in BBH gallery example
by Zach Etienne 11 Sep '25

11 Sep '25

#2706: Update default TwoPunctures parameters, or at least default parameters in BBH gallery example Reporter: Roland Haas Status: new Milestone: Version: Type: enhancement Priority: minor Component: EinsteinToolkit website Comment (by Zach Etienne): @{557058:59e031ba-9bb5-4298-a472-7b99d0ae6f22} : I have removed the string comparison in the inner loop. Also it took 12 minutes for Bitbucket to propagate my change from my branch to the PR. Unacceptable, @atlassian. -- Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2706/update-default-tw…

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#2706: Update default TwoPunctures parameters, or at least default parameters in BBH gallery example
by Roland Haas 09 Sep '25

09 Sep '25

#2706: Update default TwoPunctures parameters, or at least default parameters in BBH gallery example Reporter: Roland Haas Status: new Milestone: Version: Type: enhancement Priority: minor Component: EinsteinToolkit website Comment (by Roland Haas): Note: #2887 indicated `psi^n` is not quite what one wants it to be \(namely `(psi+u)^n`\). -- Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2706/update-default-tw…

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#2887: TwoPunctures does not support Slow-Start Lapse.
by Roland Haas 09 Sep '25

09 Sep '25

#2887: TwoPunctures does not support Slow-Start Lapse. Reporter: Zach Etienne Status: open Milestone: Version: Type: enhancement Priority: major Component: Comment (by Roland Haas): uh, looking at the pull request, I notice the difference. So #2706 should not use `initial_lapse = "psi^n"` after all. -- Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2887/twopunctures-does…

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#2887: TwoPunctures does not support Slow-Start Lapse.
by Roland Haas 09 Sep '25

09 Sep '25

#2887: TwoPunctures does not support Slow-Start Lapse. Reporter: Zach Etienne Status: open Milestone: Version: Type: enhancement Priority: major Component: Changes (by Roland Haas): responsible: [] (was ) assignee: Zach Etienne (was ) -- Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2887/twopunctures-does…

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#2887: TwoPunctures does not support Slow-Start Lapse.
by Roland Haas 09 Sep '25

09 Sep '25

#2887: TwoPunctures does not support Slow-Start Lapse. Reporter: Zach Etienne Status: open Milestone: Version: Type: enhancement Priority: major Component: Changes (by Roland Haas): status: open (was new) -- Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2887/twopunctures-does…

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#2887: TwoPunctures does not support Slow-Start Lapse.
by Roland Haas 09 Sep '25

09 Sep '25

#2887: TwoPunctures does not support Slow-Start Lapse. Reporter: Zach Etienne Status: new Milestone: Version: Type: enhancement Priority: major Component: Comment (by Roland Haas): hmm, how about: [https://bitbucket.org/einsteintoolkit/tickets/issues/2706/update-default-tw… > The BBH gallery example has a rather unusual choice of initial lapse, setting it to the average value of 1 - m\_i / \(2r\_i\) for both punctures i. More typically the initial lapse is set to the “pre-collapsed” value of psi^\{-2\} which goes like 1 - M/r at large radii for total binary mass M. This is the same asymptotic behavior that the will lapse relax to, and so this choice results in less gauge dynamics than the “averaged lapse” value. TwoPunctures supports `initial_lapse = "psi^n"` and chooses a perfectly fine default value of `n=initial_lapse_psi_exponent=-2` . ‌ -- Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2887/twopunctures-does…

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#2887: TwoPunctures does not support Slow-Start Lapse.
by Zach Etienne 09 Sep '25

09 Sep '25

#2887: TwoPunctures does not support Slow-Start Lapse. Reporter: Zach Etienne Status: new Milestone: Version: Type: enhancement Priority: major Component: Comment (by Zach Etienne): Please review -- Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2887/twopunctures-does…

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#2887: TwoPunctures does not support Slow-Start Lapse.
by Zach Etienne 09 Sep '25

09 Sep '25

#2887: TwoPunctures does not support Slow-Start Lapse. Reporter: Zach Etienne Status: new Milestone: Version: Type: enhancement Priority: major Component: Currently TwoPunctures offers several options for setting the initial lapse. None of these options are compatible with Slow-Start Lapse \[arXiv:2404.01137, Phys. Rev. D 110, 064045 \(2024\)\], which requires that the initial lapse be set to W=\(psi\+u\)^\{-2\}. Here is the PR that resolves this issue: [https://bitbucket.org/einsteintoolkit/einsteininitialdata/pull-requests/21]… -- Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2887/twopunctures-does…

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