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davidwhogg / TheTractor

contributions to and ideas about the Tractor (which mainly lives at Astrometry.net)
http://theTractor.org/
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bosch comment on alpha^ser #33

Closed davidwhogg closed 11 years ago

davidwhogg commented 11 years ago

in email 2012-10-25

davidwhogg commented 11 years ago

I am pushing this to @dstndstn: Either close this issue or check Bosch's formula with the cases in the paper. If it checks out, I would be willing to include his formula -- it is useful! But I am unwilling to include it without checking it, and I am unwilling to check it. Because I am lazy. Shoot me.

Oh, by the way, if we check this and code it in, it makes our general Sersic fitter possible, so this is a GOOD IDEA (tm).

dstndstn commented 11 years ago

I'm not sure exactly what comment you're talking about here -- I don't see an email from Jim in 2012-10-25 on this topic. Is it in his Bosch 2010 paper?

davidwhogg commented 11 years ago

copying here:

Just one very minor comment: I think it might be worthwhile to include the formula for the radius normalization $\alpha$ in the Sersic profiles, maybe in place of listing numeric values for different Sersic indices.

Here it is, since it's a pain to look up/compute:

$\alpha = \gamma_p^{-1}(2n,1/2)$

where $\gamma_p^{-1}(p,z)$ is an inverse incomplete gamma function that can be evaluated by e.g. "scipy.special.gammaincinv(p,z)".

Looks good!

davidwhogg commented 11 years ago

pinging @dstndstn

dstndstn commented 11 years ago

Just copy-n-pasted Jim's code and it works a-ok!

I'll edit the text to insert this formula.