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How to fit my data?

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irenaldo

Brazil
1 Posts

Posted - 12/30/2008 : 12:55:30 PM

Hi,

I have a problem. I want to fit my data using my own function, but when I start the fit, appear this message:
"Your fitting function is not generating value". This is my equation:

y=(P1*exp(-(pi*x*4)/P2))/(1+(x/P2)^2), where P1, P2 and P2 are free parameters.

What´s the problem? What did I do wrong?
Can Anyone help me?

Deanna

China
Posts

Posted - 12/31/2008 : 01:29:23 AM

Hi Irenaldo,

The definition looks ok to me. We have to check other settings. Please send your FDF file (function definition file) to us and also tell us the version of Origin you are using.

Instructions to send files are available here:
http://www.originlab.com/index.aspx?s=1&lm=123&pid=752

Deanna
OriginLab Technical Services

greg

USA
1379 Posts

Posted - 01/15/2009 : 11:28:21 AM

Since the equation looks fine, the message "Your fitting function is not generating value" is probably indicating you haven't given your parameters any values. All User-Defined functions must supply initial values for parameter before fitting.
If you don't have a good idea what the values should be like, just use
P1 = 1;
P2 = 2;
and use the Simplex method before using the Levenberg/Marquardt method.

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