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 partial derivatives from user fitting functions		  New Topic  Reply to Topic
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Walter Whitlock

USA
1 Posts
Posted - 10/20/2000 :  8:04:00 PM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
For non-linear least squares fitting with a user supplied fitting function, is it possible for Origin to take 1st partial derivatives from user supplied expressions instead of using numerical differentiation? I am especially interested in doing this with a DLL fitting function, but other approaches would be useful too.

rtoomey

USA
184 Posts
Posted - 10/25/2000 :  8:26:00 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply


Walter,

I don't know if this will answer your question or not (in fact I think you already knew this), but here goes...

Origin has the ability to handle partial derivatives in the fitter, but it is the partial derivatives of the parameters which are needed, not the variables.

For example, if you were to fit using the partial derivatives for the equation of a line (y = P1 + P2*x) you would have to define your fitting function in the following manner:

FormY-Script
Anal. DerivativesChecked
Definitiony'P1=1;
y'P2=x;

If this is not what you were asking, please let me know.

Sincerely,
Ryan Toomey

[This message has been edited by rtoomey (edited 10-25-2000).]
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irenevassi

USA
3 Posts
Posted - 11/13/2000 :  11:19:14 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Once Origin6.1 SR1 becomes available, Origin will be able to handle fitting functions defined in an external DLL where the expressions for the partial derivatives are given in the implementation of the function. Then Origin's NLSF will use these expressions when computing the derivatives (rather than numerical differentiation).
Also an example of a DLL with such a function will be available.
(If you can not wait for SR1, contact our technical support and we might be able to give you the example and a new version of one of our DLLs so that you can write such external DLL fitting functions)
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