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 Trouble Creating Custom Non-linear Curve Fitting
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ZY4914

USA
4 Posts

Posted - 04/09/2014 :  4:13:13 PM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
Origin Ver. and Service Release (Select Help-->About Origin): 9.1
Operating System:Window 8.1

Hi, I need help to create a non-linear curve fitting function for the following expression:

y = C + A/3*(x^2*(3-x^2/B)/(1-x^2/B))-(x-x^3)*(3-1/(x*B))/(1-1/(x*B))

where C, A, and B are positive constants I would like to get.

I have tried creating the function by inputting the above formula and setting x as independent variable, y dependent variable, C, A, and B as parameters greater than 0. However, the resulting fitting was not successful.

Thank you in advance for your comments and suggestions.

zahraa

USA
52 Posts

Posted - 04/10/2014 :  11:06:28 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi ZY4914,

Is there a specific reason you wish to use that function and not a different one? Just asking since an exponential function would fit your sample data completely, there are many built in exponential functions in Origin that worked when I tried it.

Edited by - zahraa on 04/10/2014 11:07:15 AM
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ZY4914

USA
4 Posts

Posted - 04/10/2014 :  11:21:56 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi Zahraa,

The function that I intended to use for fitting my data is an empirical expression reported by others in my filed. I am interested in exacting the constants A and B from my data.

Edited by - ZY4914 on 04/10/2014 11:24:23 AM
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ZY4914

USA
4 Posts

Posted - 04/10/2014 :  2:00:54 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Fitting can be done after setting appropriate initial values for the parameter, but very time-consuming.

I have deleted my reply with sample data set and curve.

Edited by - ZY4914 on 04/10/2014 2:02:08 PM
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