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vpresser
Germany
Posts |
 Posted - 07/15/2007 : 08:53:23 AM
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Hello,
currently, I cannot figure out why the following won't work...
1. I created a column running from -5 to +5 with a step widht of 0.25
2. I calculated the values in column 2 via:
Col(B) = 1/2 - 1/Pi*atan(-Col(A)/4) with 4 just one value for a parameter (A)
3. Plotting the data
4. Trying to fit the data with:
y=1/2-1/Pi*(atan(-x/A)); and now A should become 2
--> well... A will be refined to be 2 but the x-y-data totally derivates from the input data! In fact, I receive a sigmoidal function that is almost parallel to my input data and shifted toward smaller y-values.
Has anyone any idea what went wrong or how to fix that problem? I want to adapt this regression for real data and not only for simulated ideal values but when such deviations occur even on ideal values...
Thanks a lot! This problem is really bugging me...
Best regards,
Volker
Origin Version (7.5G) / Operating System (Vista Ultimate) |
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Mike Buess
USA
3037 Posts |
Posted - 07/15/2007 : 10:49:33 AM
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Hi Volker,
You are running your function in Origin C where 1/2 = 0. Either uncheck the Use Origin C option or rewrite the function like this...
y = 1/2.0 - 1/Pi*atan(-x/A)
Mike Buess
Origin WebRing Member |
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vpresser
Germany
Posts |
Posted - 07/15/2007 : 4:08:59 PM
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Wow, that was a fast answer :) Thank you very much - now everything works just perfectly!
Best regards,
Volker |
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clockwork84
Argentina
1 Posts |
Posted - 04/24/2012 : 5:18:22 PM
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I'm having trouble fitting an arc tangent function
Independent: x
Dependent: y
Parameter names: A,B,C,D
Function Form: Expression
Function
y = A*atan(x*B+C)+D
Intial values:
A=140
B=-0.9
C=6
D=495
Status: Failed(-207)
Fit did not converge
what could be wrong?
Pablo Lacourt
Materials Engineer |
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Hideo Fujii
USA
1582 Posts |
Posted - 04/25/2012 : 5:49:10 PM
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Hi Pablo,
Not sure, but data may be too noisy, or the initial parameter values may be good enough for hill-climbing? Have you tried the simulation to see how good these parameter values are? (Also, make sure that your parameter values works with the angle system (degree or radian) of the function?)
--Hideo Fujii
OriginLab
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Topic |
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misfitting atan-function