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From: Johan Maes <Johan.Maes_at_UGent.be>

Date: Fri, 20 Mar 2009 11:49:35 +0100

Hi all,

This may be a minor thing, well this is a minor thing, but still, I'm

wondering why in init_drift_table (in driftfac.c), the Hubble constant

is used as absolute error for the integrations. Here's a description of

adaptive gsl integration taken from

http://linux.math.tifr.res.in/manuals/html/gsl-ref-html/gsl-ref_16.html#SEC246

/This function applies an integration rule adaptively until an estimate

of the integral of f over (a,b) is achieved within the desired absolute

and relative error limits, epsabs and epsrel

/

In the code it says the absolute error is just used as a dummy, so I

guess the goal is to make it as big as possible (compared to the result)

so the above is always ok. But since the results have dimension of time,

I would rather expect some fraction of the Hubble time then...what am I

missing here? I'm doing something similar now to convert a to t, using

the integration in Gadget as an example, that's why I noticed.

Thx & cheers,

Johan

Date: Fri, 20 Mar 2009 11:49:35 +0100

Hi all,

This may be a minor thing, well this is a minor thing, but still, I'm

wondering why in init_drift_table (in driftfac.c), the Hubble constant

is used as absolute error for the integrations. Here's a description of

adaptive gsl integration taken from

http://linux.math.tifr.res.in/manuals/html/gsl-ref-html/gsl-ref_16.html#SEC246

/This function applies an integration rule adaptively until an estimate

of the integral of f over (a,b) is achieved within the desired absolute

and relative error limits, epsabs and epsrel

/

In the code it says the absolute error is just used as a dummy, so I

guess the goal is to make it as big as possible (compared to the result)

so the above is always ok. But since the results have dimension of time,

I would rather expect some fraction of the Hubble time then...what am I

missing here? I'm doing something similar now to convert a to t, using

the integration in Gadget as an example, that's why I noticed.

Thx & cheers,

Johan

-- En toen zei de kikker: "Voor mij ne kleine me stoverij, alstublieft."Received on 2009-03-20 12:11:34

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