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 #92837 is a reply to message #88075]

Wed, 09 March 2016 08:39

wlandsman
Messages: 743
Registered: June 2000

Senior Member

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.

But what if my data has -- due to noise -- some negative values? I can always use nonlinear fitting routines like mpfitfun, but performing thousands of fits this way will be much slower. I haven't been able to think of any tricks to keep the problem linear, but perhaps others have a suggestion. Thanks, --Wayne

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 13:55:25 PDT 2025

Total time taken to generate the page: 0.00405 seconds