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banani

India
1 Posts
Posted - 09/03/2018 :  11:19:13 AM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
Hello, I am using the following Cross Model equation:
y=(z0-z1)/(1+(a*x^(p)))+z1

where, z0 is to be determined.
Using Rheoplus software the data get converged whose values are;
z1=0.023716 Pa.s, a=29.847, p=0.74132 and c=97.627 as a=c^p and the z0 found to be 154.43 Pa.s

But giving the same input in origin16, the data is not converging. So I want to know my mistake...
Thanks in advance

Echo_Chu

China
Posts
Posted - 09/04/2018 :  04:40:20 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi,

I am not sure how you use Origin 2016 for the work. If you define your user-defined function for nonlinear curve fitting, please make sure you have set proper initial values for each parameter before the fitting.

However, I suggest you transform the function and then use our build-in Logistic function for the fitting.

Would you minding letting us know more about your function so that we can understand it more?
- What field is your function usually used on?
- What is the meaning of each parameters?

Echo
OriginLab Technical Support
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Echo_Chu

China
Posts
Posted - 09/07/2018 :  03:06:12 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi,

Origin supports a similar build-in function
https://www.originlab.com/doc/Origin-Help/Cross-FitFunc

It is available under Rheology category

Echo
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