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sri_87
United Kingdom
2 Posts |
 Posted - 08/02/2011 : 12:31:54 PM
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| I have cubic equation with the coefficients A,B,C and D dependent on other parameters. Is there a way to solve this equation and use the solution to fit data on origin6 or origin7. |
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Hideo Fujii
USA
1582 Posts |
Posted - 08/02/2011 : 12:46:38 PM
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Hi Sri_87.
Not sure what you meant by saying, "A,B,C and D dependent on other parameters". Are your A, B, C, and D undetermined parameters, and you want to determine them by fitting observation (x, y) data? Then, you can simply perform Polynomial Fit of Origin.
Or, A, B, C, D are given, and you want to solve A*x^3+B*x^2+C*X+D=0 ?
If so, there is a tool, "Finding Roots of Equations" in the File Exchange area in our site:
http://www.originlab.com/FileExchange/details.aspx?fid=52
It returns the (real) roots both numerically and graphically.
However, the description says that it works Origin 7.5, or higher. (I have tried this tool on my Origin 8.5.1, and it worked.)
If you don't have the access Origin 7.5 or a later version, you can download, install and try the latest Origin evaluation (demo) version from:
http://www.originlab.com/index.aspx?go=Downloads/OriginEvaluation
--Hideo Fujii
OriginLab |
Edited by - Hideo Fujii on 08/02/2011 1:01:20 PM |
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sri_87
United Kingdom
2 Posts |
Posted - 08/02/2011 : 1:55:25 PM
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Hi Hideo Fujii
A,B,C and D are my coefficients which are dependent on x. so by using the equation A*y^3+B*y^2+C*y+D=0, i would like to solve for y and fit my data.
Thank you for the links.
Regards
Sri_87 |
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larry_lan
China
Posts |
Posted - 08/04/2011 : 9:21:45 PM
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Hi:
I don't see x in your expression. What's the relationship between A, B, C, D vs. X? Looks like your didn't provide the whole expression.
Thanks
Larry |
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sr50
USA
1 Posts |
Posted - 08/06/2011 : 1:11:01 PM
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I think I'm trying to do something similar, but I'm still very unfamiliar with Origin and am encountering difficulties.
I'm trying to fit y, which is a function of variable x and a few parameters (Let's just say A, B, and C).
x is not a variable I measure, but rather it is the positive real solution to a polynomial (D*x^3 + E*x^2 + F*x + G = 0). The coefficients, D,E,F, and G are themselves derived from parameters A, B, and C and variables which I measure (let's say u and v). Thus, when parameters A, B, and C are changed, the cubic equations that define the values of x change and thus need to be solved during each iteration.
Sorry about all the letters, but basically I need Origin to read a few variables (u and v), guess a few parameters (A,B,and C), solve a cubic equation for the only positive/real root (x) for each data point, and use that solution with the guessed parameters (A,B,and C)to fit y, which is a function of x.
I hope I'm clear here. Any help at all would be appreciated. |
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larry_lan
China
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Posted - 08/11/2011 : 02:40:11 AM
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Hi:
It's hard to image what's your fitting model. Maybe it can not be fitted in Origin.
Currently, Origin can only fit explicit functions that in y = f(x) form.
Thanks
Larry |
Edited by - larry_lan on 08/11/2011 02:41:29 AM |
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Fitting Cubic equation