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Re: IDL - EXP fitting function [message #65914 is a reply to message #65905]

Thu, 26 March 2009 15:55

Christopher Thom
Messages: 66
Registered: October 2006

Member

Quoth glen_andy@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

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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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