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 Non linear curve fit		  New Topic  Reply to Topic
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taniap

Greece
2 Posts
Posted - 12/05/2023 :  09:07:47 AM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
Hello!
I am trying to fit some arrhenius plots with the non linear fitting of the origin but it keeps giving me a very high value of error. The equation that I'm using is the double exponential:
(I= IO/(1+Aexp(-E1/kbT) + Bexp(-E2/kbT)).
After trying to define the single exponential with good values of error, when I am trying to use this defined value in the double exponential the error keeps gaining high values. The tolerance factor that is used is 1E-9 and the max number of iterations is 400. Should I change something in these values? Can I reduce the error within 10%?

YimingChen

1592 Posts
Posted - 12/05/2023 :  09:37:09 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Have you manually set the initial values of the fitting parameters? Please refer to the page:
https://www.originlab.com/doc/Origin-Help/The_Reason_Why_Fail_to_Converge#Poor_initial_parameter_values

James
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taniap

Greece
2 Posts
Posted - 12/06/2023 :  06:17:58 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
quote:
Originally posted by YimingChen

Have you manually set the initial values of the fitting parameters? Please refer to the page:
https://www.originlab.com/doc/Origin-Help/The_Reason_Why_Fail_to_Converge#Poor_initial_parameter_values

James


Hello,
yes i have tried fixing some of the initial parameters. I wonder if by changing the tolerance factor it will still be the same. In addition, do you know if there is any option to limit the error while fitting by defining the value in the settings of the non-linear fit?
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YimingChen

1592 Posts
Posted - 12/06/2023 :  11:18:26 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Changing the tolerance factor won't help if the fitting is already converged. Could you share your data here? Thanks.

James
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