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Re: Newbie's question [message #45898]

Thu, 20 October 2005 17:07

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Thu, 20 Oct 2005 13:18:52 -0700, ChiChiRuiz@gmail.com wrote:

> Poly_fit doesn't really give me what I need. I don't need the
> coefficients of a quadratic equation, I want to know the best fit of the
> scatter plot to some power of x. I know it's not exactly power square,
> but it should be in that neighborhood. Even if I shift all data to the
> positive axis, i.e. y = a* (x-x0)^b, any x values less than x0 is still
> considered "negative". I don't know what else...maybe I'll try change of
> variable or something... thank you for your help.

Fitting to a single power law is a time honored tradition in many of
the precision-limited fields of physics (e.g. astronomy). The typical
approach is to fit a straight line to the log/log representation of
the data. The slope of the line is the exponent b. If your data have
negative values by artificial choice (e.g. time offset, etc.) simply
shift that choice to make them positive.

JD

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[Message index]

		Re: Newbie's question By: JD Smith on Thu, 20 October 2005 17:07
		Re: Newbie's question By: James Kuyper on Thu, 20 October 2005 15:08
		Re: Newbie's question By: ChiChiRuiz@gmail.com on Thu, 20 October 2005 13:18
		Re: Newbie's question By: James Kuyper on Thu, 20 October 2005 11:41
		Re: Newbie's question By: Paolo Grigis on Thu, 20 October 2005 08:10
		Re: Newbie's question By: Paul Van Delst[1] on Thu, 20 October 2005 07:10
		Re: Newbie's question By: ChiChiRuiz@gmail.com on Thu, 20 October 2005 06:53
		Re: Newbie's question By: Paul Van Delst[1] on Thu, 20 October 2005 06:44
		Re: Newbie's question By: peter.albert@gmx.de on Thu, 20 October 2005 04:02
		Re: Newbie's question By: Paolo Grigis on Thu, 20 October 2005 00:33
		Re: Newbie's question By: ChiChiRuiz@gmail.com on Fri, 21 October 2005 09:58
		Re: Newbie's question By: James Kuyper on Fri, 21 October 2005 05:55

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