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TracieJC
UK
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 Posted - 02/22/2005 : 09:23:26 AM
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Hi
I've been struggling with the non linear data fitting option in Origin for the last couple of days - I don't have a great deal of experience using Origin, so please bear this in mind if I have made a painfully obvious mistake.
I have a set of raw data that I would like to fit to the function y=K'[1-exp(-kx)]. My data consists of y as a function of x (surface coverage as a function of time, to be exact). I have read through the help files in Origin, and entered my equation as a new function. My problems begin when I try and get Origin to fit my data to this curve - I get an error message saying to check that my data sets have values, or to check for a syntax error in my equation. I've spent so much time trying to work this out, I've now confused myself beyond belief. Is what I am trying to do possible using Origin, and can anyone more experienced than I see where I am going wrong with it please?
Thank you.
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Mike
USA
357 Posts |
Posted - 02/22/2005 : 09:37:38 AM
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Hi TracieJC,
Are you remembering to use the * character to signify the multiplication operation? Origin does not recognize an implied operator (e.g. -kx must be written -k*x).
Mike
OriginLab |
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TracieJC
UK
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Posted - 02/23/2005 : 04:57:28 AM
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Thanks for that Mike. That was one of the problems, in addition I was missing a bracket so Origin did not recognise my equation.
I have now had some success with the curve fitting, although I do keep getting 'Error 28037 - initialisation parameters poorly defined' when I try and fix the parameter 'k' and modify 'K'. Is there a way around this please? I'm not entirely sure what the error is percieved to be. |
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Mike
USA
357 Posts |
Posted - 02/23/2005 : 09:17:12 AM
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This error message is a bit cryptic but I'm guessing that you are either having trouble with initial parameter estimates or perhaps your function isn't appropriate to your data.
There are others who are certainly better with Origin's nonlinear fitter than I am, and I will try to get them to throw in on this.
Mike
OriginLab |
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Non Linear Data Fitting - Help