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sombrancelha

Brazil
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Posted - 08/30/2008 :  3:48:13 PM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
Hello,
I'm using Origin 8 and I'd like some help to fit a curve into my points.

I want to fit something in the form:

y = A*ln(B*x+1)

How can I do that?

Also, for the calculation of the precision of A and B, it's important that it considers both errors in X and in Y.

Thanks in advance.

Deanna

China
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Posted - 08/31/2008 :  10:20:25 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi Sombrancelha,

You can create a user-defined function in the form you need and then use it in the Non-Linear Curve Fitting dialog to perform the fitting. Please see here for details on how to define a user-defined function:
http://www.originlab.com/www/helponline/Origin8/en/origin.htm#Regression_and_Curve_Fitting/User-Defined_Fitting_Functions.htm

I am sorry that current version of Origin does not support fitting with X errors. We apologize for the inconvenience. We are considering adding this feature in our next version.

Deanna
OriginLab Technical Services
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sombrancelha

Brazil
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Posted - 09/01/2008 :  7:08:47 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Does Origin supports fitting with X errors for the built-in functions, such as y = ax + b?
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Fay_Guo

China
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Posted - 09/02/2008 :  06:04:11 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi Sombrancelha,

I am sorry to tell you that current version of Origin does not support fitting with X errors for the build-in functions.

While Origin supports two methods of using Y error as value for weights.
For more information about it, please see here:
http://www.originlab.com/www/helponline/Origin8/en/origin.htm#Regression_and_Curve_Fitting/Simple_Linear_Regression_Dialog.htm#Fit_Options


Thanks
Fay
Originlab Technical Services
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