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Re: Explanation for keywords of POLY_FIT? [message #63137 is a reply to message #63085]

Wed, 29 October 2008 06:50

Jeremy Bailin
Messages: 618
Registered: April 2008

Senior Member

> I am looking for an explanation for some of the keywords of POLY_FIT.
> I understand SIGMA. But what are YERROR and YBAND in the mathematical
> sense? How are these values calculated? And how does MEASUREMENT_ERROR
> influence these output values?

It's been a while since I used it, so this is just off the top of my
head being refreshed by looking at the help page - I wouldn't be
shocked if it's wrong:

If your data points are X, Y and the fit is X, YFIT, then YERROR =
stddev(Y - YFIT).

The estimated error on the values YFIT is YBAND.

MEASUREMENT_ERROR only influences these via changes to YFIT, but the
form is complicated and depends on the degree of the polynomial... if
you need the detailed expression, I'd just follow the NR derivation
for linear least squares fit with whatever degree polynomial you need.

-Jeremy.

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[Message index]

		Explanation for keywords of POLY_FIT? By: Karlo Janos on Tue, 28 October 2008 09:41
		Re: Explanation for keywords of POLY_FIT? By: Jeremy Bailin on Wed, 29 October 2008 06:50
		Re: Explanation for keywords of POLY_FIT? By: Karlo Janos on Thu, 30 October 2008 01:06
		Re: Explanation for keywords of POLY_FIT? By: Jeremy Bailin on Thu, 30 October 2008 04:48

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