Re: Tabulated Power Spectrum and Initial Conditions

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From: Héctor Aceves <aceves_at_astro.unam.mx>
Date: Sat, 29 Jun 2013 16:50:47 -0700

Hi...

>
> I have a couple of questions in this topic, sorry for the inconveniences.
> Comments are welcomed.
>
> First, I am a bit confused by the comment: "Right. (And note that the
> code will use P'(k) = k^(PrimordialIndex-1) * P(k) as actual power spectrum
> for
> the ICs, and this is also what's appearing then in inputspec_ics.txt) "
> [...V. Springel]
>
> Say I have a tabulated spectrum P(k) from CAMB at z=49, properly normalized
> to the standard definition of Sig8 (say to 0.816 at z=0) and where I used
> as input parameter the spectral index 0.968, that I plan to use in N-GenIC
> with ReNormalizeInputSpectrum=0. I understand that the P(k) from CAMB is
> the P'(k) [P prime] you indicate above, isn't? So one just has to provide
> in the tabulated file two columns "log k , log [ 4 Pi k^3 P(k)]" with P(k)
> being the one -for example- from CAMB, isn't?
>
> Secondly, by using the option given in the input parameter file for
> N-GenIC:
> InputSpectrum_UnitLength_in_cm 3.085678e24 ; one can safely input the
> wave-number k in [h/Mpc] units directly from CAMB, isn't?
>
>
> Thirdly.. when one uses ReNormalizeInputSpectrum=0, all the sigma^2
> definitions appear irrelevant in this case, isn't? Since I understand that
> the Sigma computation is for normalization purposes essentially. In any
> case, I assume one can compute Sigma directly from the initial snapshot,
> after obtaining its power spectrum directly from the data, and compare it
> to the expected value.
>
> Thanks for your time and patience :-)
>
> -Hector
>
>

> On Fri, Jun 28, 2013 at 7:29 AM, Volker Springel <
> volker_at_mpa-garching.mpg.de
> > wrote:
>
> > >> Right. (And note that the code will use P'(k) = k^(PrimordialIndex-1)
> *
> > P(k) as actual power spectrum for the ICs, and this is also what's
> > appearing then in inputspec_ics.txt)
> > >>
>
>
Received on 2013-06-30 02:20:43