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Alexander_1987

Germany
1 Posts

Posted - 07/17/2011 : 1:09:43 PM

Origin Ver. and Service Release (Select Help-->About Origin): 8.5
Operating System: Windows XP

Dear all,
I am a complete beginner in this, and therefore I tried to follow the tutorial to create function: a=a0+k*D^n
here is the tutorial to a bit different function: http://qhwiki.originlab.com/~originla/howto/index.php?title=Tutorial:User_Defined_Fitting_Function_using_OC

However this tutorial says to enter some initial values of parameters.
Can somebody explain to me what does this mean? I have no idea what my initial values are. I just have experimental plot and this function.
All I get is a red message that parameters were out of range :(

I look forward to replies.
Kindest Regards,
Alexander

larry_lan

China
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Posted - 07/18/2011 : 02:34:05 AM

Hi:

The Levenberg-Marquardt iterative algorithm (Which is used in Origin to fit a curve) requires initial values to start the fitting procedure. You can see some information from here

http://en.wikipedia.org/wiki/Levenberg%E2%80%93Marquardt_algorithm

Actually, you don't need to totally understand the math. These values are just some initial guess, you can put some values which you think are close to the final fitted results. Or, the fitter will not start. If you really have no ideas for the values, try 1 may help sometimes.

Thanks
Larry
OriginLab

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