Lorentz fit of a curve with Lev-Mar

Hello everybody! I am trying to set of data to a Lorentz curve to calculate a Q value (resonance.) I found a program on a thread from this forum that appears to work with the sample data set from the thread. However, when I try to run the program using my data set with known fitted coefficients as the initial guesses, we get an error in the Lev-Mar sub-VI -- something like “the input matrix is singular”. There’s a screenshot of my data in in the attached zip folder, as well as the text file containing my data.
My data curves down (reaching a minimum) instead of up, as in the sample data set, but it seems like that should be accounted for by the different initial guesses. I am thinking that something else is going on; hopefully it is something simple that I am just missing. Any help y'all can provide would be greatly appreciated!
Thank you!
Attachments:
Lorentz Fit.zip ‏1992 KB

Hello Lynn,
Yes, there are quite a few potential peaks in that data set. The peak you identified was the one that we are trying to fit (The peak should be trimmed by the cursors.) We used origin to fit that same peak in order to get the initial guesses for the coefficients in the screenshot. When it runs, we get the error message: "Error -20041 occured at NI_Gmath.lvlib: Nonlinear Curve Fit LM.vi:2 Possible reason(s): Analysis: The system of equations cannot be solved because the input matrix is singular."
Thanks!
-Garrison

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Attachments:
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fit2.png ‏30 KB
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帖子被myafu在12-22-2006 01:33 AM时编辑过了

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Solved!
Go to Solution.
Attachments:
error2.vi ‏13 KB
FittingGaussianKnife.vi ‏15 KB

Try this. Seem to work just fine (LabVIEW 2013).
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===Please see the attached vi file===
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Lev-Mar-Question2.vi ‏99 KB

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Nonlinear Fit Lev-Mar.Berry.vi ‏41 KB
simple sine model.vi ‏21 KB

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Message Edited by urumilton on 01-14-2009 10:28 AM
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Lorentz fit of a curve with Lev-Mar

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