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 Logistic Equation in Originpro		  New Topic  Reply to Topic
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ezx6987e

Singapore
2 Posts
Posted - 05/11/2015 :  12:19:04 PM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
Origin Ver. and Service Release (Select Help-->About Origin):
Operating System:9.1.0 (64 bits)

I'm a new user in Originpro and try to do a sigmoidal curve fitting of my data. I have problem in understanding the general solution of logistic equation as y=A2*A1/(A1+(A2-A1)*exp(-rx)) and compared to the equation in Originpro given as y=A2+(A1-A2)/(1+(x/xo)^p).

Hopefully someone there kind enough to advice on my doubt. Thanks.

lkb0221

China
497 Posts
Posted - 05/11/2015 :  3:59:44 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi,

There are many kinds of logistic curves. You can try SLogistic3.
http://www.originlab.com/doc/Origin-Help/SLogistic3-FitFunc


Zheng
OriginLab
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ezx6987e

Singapore
2 Posts
Posted - 05/11/2015 :  11:29:09 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi Zheng,

Appreciate your reply on this matter. For the logistic equation in the originpro which given as y=A2+(A1-A2)/(1+(x/xo)^p), any reference on how to derive this equation? This is because i could not find the relevant information.

Thanks!
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lkb0221

China
497 Posts
Posted - 05/12/2015 :  5:32:09 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
It's a 4PL equation:
http://psg.hitachi-solutions.com/masterplex/blog/the-4-parameter-logistic-4pl-nonlinear-regression-model
http://www.myassays.com/four-parameter-logistic-curve.assay
https://www.medcalc.org/manual/nonlinearregression_example.php
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