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noazn

Israel
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Posted - 09/12/2007 :  05:35:22 AM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
How can I fit two sets of data to two different functions but with the same parameters?

Mike Buess

USA
3037 Posts

Posted - 09/12/2007 :  12:41:10 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
You must create a third fitting function with two dependent variables. If the datasets share the same X column you can get away with one independent variable as shown in the top figure which illustrates the approach for two hypothetical functions, funcA and funcB, each with two parameters, a and b. If the X values are different you'll need two independent variables, xA and xB.

Of course the details are in how to express the functions. If you created both functions yourself you'll just have to write them out completely. Built-in fitting functions have corresponding LabTalk functions which can be used to shorten the expressions. You can find the LabTalk functions for built-in fitting functions here...

http://www.originlab.com/pdfs/curvefittingfunctions.pdf

If you have O70 or O75 I suggest you use OriginC, in which case the LabTalk functions cannot be called directly... The bottom figure shows how to use LabTalk's Lorentz and Gauss functions in OriginC.





Mike Buess
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noazn

Israel
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Posted - 09/12/2007 :  4:47:46 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Thank you, you have been most helpful.
Can you advise me on how to make a fit to a 3D function?

Noaz.
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Mike Buess

USA
3037 Posts

Posted - 09/12/2007 :  5:10:57 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
These two articles might help...

http://www.originlab.com/www/support/resultstech.aspx?ID=128&language=English&Version=All

http://www.originlab.com/index.aspx?s=9&pid=434

Mike Buess
Origin WebRing Member
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