[Users] evolving a BH hole with Kerr-Schild ID in ET

[Haas, Roland]

Hello Erik,

> This is almost possible. For puncture data, one typically evolves
> lapse, shift, and a quantity B (the time derivative of the shift). For
> Kerr-Schild data, one also needs to evolve A, the time derivative of
> the lapse. Otherwise, Kerr-Schild data are not stationary. (One could
> instead add an offset alpha_0 to the evolution equations for K, but
> that is quite non-standard and not implemented in McLachlan.)
Ok so it is possible.

> Additionally, I find it convenient to smooth all quantities near the
> singularity, and to choose to advect both lapse and shift. I don't
> know whether the latter is necessary in theory, but I am always using
> it.
Concerning the smoothing it seems that some smoothing was necessary to
not crash the code (via the Exact epsilon parameter to transform r ->
r+epsilon). An alternative may have been to use NoExcision to fill the
interior of the AH with smooth data.

> I can send a sample parameter file if that helps.
That would be great if you had something that you could send around
easily.

Yours,
Roland

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