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Re: IDL - EXP fitting function [message #65905 is a reply to message #65901]

Thu, 26 March 2009 19:11

Vince Hradil
Messages: 574
Registered: December 1999

Senior Member

On Mar 26, 5:55 pm, Christopher Thom <ct...@oddjob.uchicago.edu>
wrote:
> Quoth glen_a...@hotmail.com:
>
>
>
>> On Mar 26, 5:12 pm, David Fanning <n...@dfanning.com> wrote:
>>> glen_a...@hotmail.com writes:
>>>> Greetings everyone! My first post! I have some data x, y, that i would
>>>> like to fit to a fitting function of the kind yfit = EXP(a+ b*x).
>>>> where a and b are constants which i would like found. Any ideas on how
>>>> to do this?
>
>>> ab = LinFit(x, y)
>>> a = ab[0]
>>> b = ab[1]
>
>>> Cheers,
>
>>> David
>>> --
>>> David Fanning, Ph.D.
>>> Fanning Software Consulting, Inc.
>>> Coyote's Guide to IDL Programming:http://www.dfanning.com/
>>> Sepore ma de ni thui. ("Perhaps thou speakest truth.")
>
>> Thanks for getting back to me David,
>
>> Does the linfit function work when i would like my data to be fitted to
>> an EXP(a + bx) function? I didn't think that a linear function would be
>> correct when considering the EXP? Or am i getting confused going from
>> real space to log space!
>
> No, linfit() fits a linear model of the form y = A + B*x, so it will not
> "just work". why don't you just fit a linear model in logspace?
>
> res = linfit(x, alog(yfit))
> a = res[0]
> b = res[1]
>
> cheers
> chris

I'll second that. This is really a linear problem, so no need to
solve the non-linear equation.

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[Message index]

		Re: IDL - EXP fitting function By: glen_andy on Fri, 27 March 2009 09:13
		Re: IDL - EXP fitting function By: Vince Hradil on Fri, 27 March 2009 07:03
		Re: IDL - EXP fitting function By: pgrigis on Fri, 27 March 2009 06:50
		Re: IDL - EXP fitting function By: Vince Hradil on Fri, 27 March 2009 06:38
		Re: IDL - EXP fitting function By: pgrigis on Fri, 27 March 2009 06:27
		Re: IDL - EXP fitting function By: Maarten[1] on Fri, 27 March 2009 03:13
		Re: IDL - EXP fitting function By: Vince Hradil on Thu, 26 March 2009 19:11
		Re: IDL - EXP fitting function By: Christopher Thom on Thu, 26 March 2009 15:55
		Re: IDL - EXP fitting function By: glen_andy on Thu, 26 March 2009 15:33
		Re: IDL - EXP fitting function By: glen_andy on Thu, 26 March 2009 15:25
		Re: IDL - EXP fitting function By: David Fanning on Thu, 26 March 2009 15:15
		Re: IDL - EXP fitting function By: David Fanning on Thu, 26 March 2009 15:12

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