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LCG
Canada
9 Posts |
 Posted - 06/26/2012 : 8:17:47 PM
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Hello,
I'm using Origin Lab version 7.0, SR2. I wrote in a function that compiles but it won't fit my data. I'm hoping it's just a small mistake that I'm overlooking. Any help I can get with this will really be greatly appreciated. I have written the equation, including the parameters and a data set below.
Thank you for your help,
Q=(((P4*(H+P2)+1)-((P4*(H+P2)-1)^(2))-4*((P4^(2))*H*P2)^(0.5))*((P5-P6)+P2*P6))/(2*P4*P2)
Where Q= Dependent Variable H= Independent Variable P2,P4,P5,P6= Parameters where P2=0.5 and does not vary, P4=9e6 and does vary, P5=27 and does not vary and P6= -1694 and does not vary.
H Q
0 0
0.005 26.8
0.025 -25
0.1 -232
0.2 -503
0.3 -760
0.5 -1114
1.25 -1599
1.5 -1603
2.5 -1669
3.5 -1685
5 -1695
Thank you
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Hideo Fujii
USA
1582 Posts |
Posted - 06/27/2012 : 11:40:04 AM
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Hi LCG,
> Q=(((P4*(H+P2)+1)-((P4*(H+P2)-1)^(2))-4*((P4^(2))*H*P2)^(0.5))*((P5-P6)+P2*P6))/(2*P4*P2)
> ...P2,P4,P5,P6= Parameters where
> P2=0.5 and does not vary,
> P4=9e6 and does vary,
> P5=27 and does not vary and
> P6= -1694 and does not vary.
The curve with these initial values seems far away from your data.
See the screenshot below. Graph1 is the plot of your data,
and Function1 is the initial fitted curve - both Y range of the function and
the shape of the curve are away from your data - it seems for me that
either you should find better initial values, or your model function is not appropriate.
Hope my observation is helpful.
--Hideo Fujii
OriginLab
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LCG
Canada
9 Posts |
Posted - 07/05/2012 : 2:12:30 PM
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Thanks for your help Hideo! I'm still stuck but I'm not really sure why. What does it mean to have the numbers stop changing but no red line is fitting. I'm trying another equation and the number I'm looking for ( the varying parameter) gets close to a number I know it should be but there is no red line actually fitting to the data. Also one more question, is there a source I can go to for creating a new model? Is there such a forum where I can get help creating a new equation?
Thank you :) |
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Non-Linear Curve fitting function won't fit data