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 Non Linear curve fitting problem		  New Topic  Reply to Topic
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Markec30

1 Posts
Posted - 06/20/2011 :  6:51:22 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:
Hello;
I have got a problem with this non linear fitting which works fine in Origin 7, but in Origin 8 dose not. The program is following:

Independent variables: x

Dependent variables: y

Parameter names: a,do,d,dm

y=d*6*(1-exp(-(do*x/d)^a))^(1/a)*(1+(dm*x/d))

So this program can not be fitted till the end as in Origin 7.
Can you please help me with this problem.
Thank you in advance.
Marko

Hideo Fujii

USA
1582 Posts
Posted - 06/20/2011 :  7:31:03 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi,

Maybe you can follow the procedure like in this document?:

http://wiki.originlab.com/~originla/howto/index.php?title=Tutorial:User_Defined_Fitting_Function_using_OC

Please check whether the function's correctness at its Step 3.

In many cases of failure of fitting using a user defined function, the initial parameter values are not good enough in terms of the closeness to the target function. (In NLFit, you can press Chi^2 button when it starts fitting to see the current estimated curve.)

Hope this suggestion is helpful.

--Hideo Fujii
OriginLab
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