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 How does fitparams obtain the sigma column?
 05/05/2017 01:53AM (Read 331 times)  
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Registered: 10/10/2008
Posts: 104
I'm trying to reproduce the 'sigma' column returned by the photcal.fitparams task (http://stsdas.stsci.edu/cgi-bin/gethelp.cgi?fitparams); see page 32 of the guide:


Following the trace, I see that the 'iraf/pkg/xtools/inlfit/ingresults.gx' file writes to that column the following values:

(sqrt (PIXEL (1.0) / Mem$t[wts1+i-1]))

I assume 'Mem$t[wts1+i-1]' is some kind of standard deviation? How can I reproduce the values in that column manually?

Also, since I'm at it, how is the 'average scatter' value obtained (also shown in the above mentioned page)? I tried:

mean(abs(function - fit))

but I can't reproduce the values shown there.

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