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Biotec12
Armenia
8 Posts |
 Posted - 06/30/2011 : 04:52:14 AM
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Dear friends,
I am trying to fit a curve to a data points using Origin 7.
here are my data points
0 0
3.34303E-6 8.537E-8
4.66962E-6 1.2195E-7
5.99623E-6 1.7073E-7
7.32282E-6 2.561E-7
8.64942E-6 3.2927E-7
9.97601E-6 3.9146E-7
1.13026E-5 5.0122E-7
1.26292E-5 5.8659E-7
1.39558E-5 6.7317E-7
1.52824E-5 7.9634E-7
1.6609E-5 8.9512E-7
1.79356E-5 1.01098E-6
1.90499E-5 1.10976E-6
and here is the function to which I want to fit
C*(sin(k*x)-(A/(2.796*10^-29*k))*(1+(sin(k*19.05*10^-6)-(A/(2.796*10^-29*k))*cos(k*19.05*10^-6)-(A/2.796*10^-29*k))*cosh(k*19.05*10^-6))/(sinh(k*19.05*10^-6)+(A/(2*(1.398*10^-29)*k))*cos(k*19.05*10^-6)+(A/(2*(1.398*10^-29)*k))*cosh(k*19.05*10^-6)))*cos(k*x)+((sin(k*19.05*10^-6)-(A/(2.796*10^-29*k))*cos(k*19.05*10^-6)-(A/2.796*10^-29*k))*cosh(k*19.05*10^-6))/(sinh(k*19.05*10^-6)+(A/(2*(1.398*10^-29)*k))*cos(k*19.05*10^-6)+(A/(2*(1.398*10^-29)*k))*cosh(k*19.05*10^-6)))*sinh(k*x)+(A/(2.796*10^-29*k))*(1+(sin(k*19.05*10^-6)-(A/(2.796*10^-29*k))*cos(k*19.05*10^-6)-(A/2.796*10^-29*k))*cosh(k*19.05*10^-6))/(sinh(k*19.05*10^-6)+(A/(2*(1.398*10^-29)*k))*cos(k*19.05*10^-6)+(A/(2*(1.398*10^-29)*k))*cosh(k*19.05*10^-6)))*cosh(k*x))
Fitting constants are A,k and C
initial values are A = 7.31707*10^-24; k =862467 and C =2.7385*10^8
I am getting message:
Unable to compile user defined function
I will really appreciate if you will help me to fit the curve, using even two parameters k and A will be enough for me just delete C from formula.
Best
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Hideo Fujii
USA
1582 Posts |
Posted - 06/30/2011 : 10:23:01 AM
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Hi Biotec12,
First of all, it seems your formula's parentheses don't match (if my checking is correct).
Also, as your function form doesn't have the left-hand side with the dependent variable like "y=", check that the form of the fit function is "Expression"; However, I strongly suggest to set the form to "Origin C" rather than "Expression" for such a complected function so that you can divide your function into the combination of multiple terms - to avoid the parenthesis mismatch and easy to maintain. (Also, since 19.05*10^-6 seems to be a common constant in your function, it would improve the readability if you define it as a constant.)
--Hideo Fujii
OriginLab |
Edited by - Hideo Fujii on 06/30/2011 10:25:17 AM |
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easwar
USA
1965 Posts |
Posted - 06/30/2011 : 11:31:45 AM
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Hi,
Also change numbers such as "19.05*10^-6" to "19.05E-6", this was an issue in older versions in OC functions.
Easwar
OriginLab |
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Biotec12
Armenia
8 Posts |
Posted - 06/30/2011 : 2:58:08 PM
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Thanks a lot for reply however, I am still getting same massage
Unable to compile user defined function
y=C*(sin(k*x)-(A/(2.796E-29*k))*(1+(sin(k*19.05E-6)-(A/(2.796E-29*k))*cos(k*19.05E-6)-(A/2.796E-29*k))*cosh(k*19.05E-6))/(sinh(k*19.05E-6)+(A/(2*(1.398E-29)*k))*cos(k*19.05E-6)+(A/(2*(1.398E-29)*k))*cosh(k*19.05E-6)))*cos(k*x)+((sin(k*19.05E-6)-(A/(2.796E-29*k))*cos(k*19.05E-6)-(A/2.796E-29*k))*cosh(k*19.05E-6))/(sinh(k*19.05E-6)+(A/(2*(1.398E-29)*k))*cos(k*19.05E-6)+(A/(2*(1.398E-29)*k))*cosh(k*19.05E-6)))*sinh(k*x)+(A/(2.796E-29*k))*(1+(sin(k*19.05E-6)-(A/(2.796E-29*k))*cos(k*19.05E-6)-(A/2.796E-29*k))*cosh(k*19.05E-6))/(sinh(k*19.05E-6)+(A/(2*(1.398E-29)*k))*cos(k*19.05E-6)+(A/(2*(1.398E-29)*k))*cosh(k*19.05E-6)))*cosh(k*x)) |
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Hideo Fujii
USA
1582 Posts |
Posted - 06/30/2011 : 3:42:41 PM
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Hi,
I have counted ('s and )'s. There are 63 ('s and 66 )'s. So, obviously parentheses are not matched. Again, I suggest you to divide it to multiple terms.
--Hideo Fujii
OriginLab |
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Biotec12
Armenia
8 Posts |
Posted - 07/03/2011 : 10:01:55 AM
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Thanks a lot I correct the parentheses, now I am getting large error bars
Data: Data1_D
Model: user2
Weighting:
y No weighting
Chi^2/DoF = 5.5384E-16
R^2 = 0.99639
k 7.75826 +-19653.00291
A 7.5527E-18 +-2.303E-14
C 547047.41189 +-4178111280.25768
do you have any idea what could be the problem ?
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Biotec12
Armenia
8 Posts |
Posted - 07/05/2011 : 04:29:19 AM
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| Pleas reply. |
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Hideo Fujii
USA
1582 Posts |
Posted - 07/05/2011 : 4:25:06 PM
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Hi,
I suspect that your initial parameter values are not good enough to give a reasonably close curve to start fitting your data. You can see the curve of the current parameter values on the graph by pressing "Chi^2" button in NLFit tool, or you can use the "Simulate" button in the Fitting Function Organizer to evaluate the parameter values. In many cases with a user-defined function, the divergence is the result of not-good-enough initial parameter values.
--Hideo Fujii
OriginLab |
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Topic |
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Curve fitting