comp.lang.idl-pvwave archive: archive » power law fit with a constant

Home » Public Forums » archive » power law fit with a constant

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: power law fit with a constant [message #92843 is a reply to message #92837]

Thu, 10 March 2016 09:40

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

On Wednesday, March 9, 2016 at 11:39:29 AM UTC-5, wlandsman wrote:
> On Tuesday, March 18, 2014 at 10:13:47 PM UTC-4, suruchi wrote:
>> Could anyone suggest me how to do the fitting of the following functions:
>>
>> 1) A + B (x^gamma) which is a power law with a constant.
>>
>> without the constant, for the power law of the form " Bx^gamma " it is easy to convert to log space and linearize the problem, that is
>> log(y)=log(B)+gamma*(log(x)).
>
> I am trying to fit a power law without the constant term to data. As noted above, and also at
> http://www.exelisvis.com/Support/HelpArticlesDetail/TabId/21 9/ArtMID/900/ArticleID/2813/2813.aspx
> one can convert to log space and linearize the problem. This is very nice because linear fits can be vectorized and I can do a million linear fits in one vector call.
...

Wayne, the fit is "linear" in the values, but non-linear if one considers the error bars. That would not be a large problem if the significance of the data was always large, but since you mention negative values, some of your values must be very low significance. I think you need to do a non-linear fit to capture the errors properly.

Craig

Report message to a moderator

[Message index]

		power law fit with a constant By: suruchi on Tue, 18 March 2014 19:13
		Re: power law fit with a constant By: Craig Markwardt on Tue, 18 March 2014 19:59
		Re: power law fit with a constant By: wlandsman on Wed, 09 March 2016 08:39
		Re: power law fit with a constant By: Craig Markwardt on Thu, 10 March 2016 09:40
		Re: power law fit with a constant By: wlandsman on Thu, 10 March 2016 10:25

Previous Topic:	How can I write the following exponential function in idl
Next Topic:	INTERPOLATE function - Question

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Wed Oct 08 18:18:57 PDT 2025

Total time taken to generate the page: 0.00460 seconds