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Re: Logistic model in COMFIT function [message #93813 is a reply to message #93810]

Wed, 26 October 2016 07:24

Dick Jackson
Messages: 347
Registered: August 1998

Senior Member

On Tuesday, 25 October 2016 13:37:22 UTC-7, bedro...@gmail.com wrote:
> Hi,
>
> I am currently using the logistic model in COMFIT. The results are good; however, when I read the equation IDL uses for logistic model, I got confused. The equation is: y=1/(a0a1^x+a2). I can not understand why a0 and a1 are necessary? They can be combined as one empirical parameter. How does each of the empirical parameter work in this IDL function?
>
> If you can provide any thought, I will greatly appreciate.
>
> Thank you.
>
> Sincerely,
> Nick

Hi Nick,

To make that equation clearer, to show the order of operations when it is evaluated (exponents before multiplication), it could be written as:

y = 1 / ( ( a0 * (a1^x) ) + a2 )

Does that help to show how a0 and a1 are quite distinct?

Cheers,
-Dick

Dick Jackson Software Consulting Inc.
Victoria, BC, Canada --- http://www.d-jackson.com

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[Message index]

		Logistic model in COMFIT function By: bedroom330 on Tue, 25 October 2016 13:37
		Re: Logistic model in COMFIT function By: Dick Jackson on Wed, 26 October 2016 07:24
		Re: Logistic model in COMFIT function By: dcleuclidwl on Wed, 26 October 2016 07:28

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