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grey_fit
USA
3 Posts |
 Posted - 02/18/2019 : 2:59:18 PM
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I'm trying to fit solved differential equations to kinetics data and origin will crash with very long equations. The equations are solved in maple and imported into origin as a user defined nonlinear function. The issue with the differential equations is the solution length increases greatly with every paired term.
Is there a way around the equation limit in origin? Can I represent the solution in a different form origin can handle? Is there a better way to do the fitting? Thanks in advance.
Example maple input:
diff(a(x), x) = -k1*a(x), diff(b(x), x) = k1*a(x)-k1*b(x), diff(c(x), x) = k1*b(x)-k1*c(x),
diff(d(x), x) = k1*c(x)-k2*d(x),
diff(e(x), x) = k2*d(x)-k3*e(x), diff(f(x), x) = k3*e(x)-k3*f(x), diff(g(x), x) = k3*f(x)-k3*g(x), diff(h(x), x) = k3*g(x)-k3*h(x), diff(i(x), x) = k3*h(x)-k3*i(x), diff(j(x), x) = k3*i(x)-k3*j(x), diff(k(x), x) = k3*j(x)-k3*k(x),
a(0) = 1, b(0) = 0, c(0) = 0, d(0) = 0, e(0) = 0, f(0) = 0, g(0) = 0, h(0) = 0, i(0) = 0, j(0) = 0, k(0) = 0;
Example output:
https://pastebin.com/raw/DYZwzpW4
Origin Ver. and Service Release (Select Help-->About Origin): 2018 64bit SR1
Operating System: Windows 10 |
Edited by - grey_fit on 02/18/2019 3:44:12 PM |
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Castiel
343 Posts |
Posted - 02/19/2019 : 02:38:41 AM
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quote:
Originally posted by grey_fit
The equations are solved in maple and imported into origin as a user defined nonlinear function.
How you defined the fitting function seems to cause the problem. Hardly can one solve the problem without the FDF file and the data. You may provide them as well.
&&&&&&&&&
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& _____ ___________
II__|[] | | I I |
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< OO----OOO OO---OO
**********************************************************
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grey_fit
USA
3 Posts |
Posted - 02/19/2019 : 12:51:10 PM
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| I should clarify origin crashes when you save the fit, not when fitting to data. |
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Castiel
343 Posts |
Posted - 02/19/2019 : 5:35:14 PM
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quote:
Originally posted by grey_fit
I should clarify origin crashes when you save the fit, not when fitting to data.
How was the user defined nonlinear function 'imported'?
IIRC there is no way to 'import' as Origin FDF. In most cases, you should define the fitting function manually.
&&&&&&&&&
&&&
&&
& _____ ___________
II__|[] | | I I |
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< OO----OOO OO---OO
**********************************************************
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grey_fit
USA
3 Posts |
Posted - 02/21/2019 : 4:08:16 PM
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| Right, the fitting function was defined manually. However, the fitting function is quite large (>5,000 characters long). Is there a limit on the size of the user defined fitting function? |
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Castiel
343 Posts |
Posted - 02/21/2019 : 10:15:41 PM
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quote:
Originally posted by grey_fit
Right, the fitting function was defined manually. However, the fitting function is quite large (>5,000 characters long). Is there a limit on the size of the user defined fitting function?
You can define a fitting function in multiple way. You should not simply copy the results from maple and paste it in Origin.
You should try to define the fitting function in Origin C.
&&&&&&&&&
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& _____ ___________
II__|[] | | I I |
| |_|_ I I _|
< OO----OOO OO---OO
**********************************************************
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Echo_Chu
China
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Posted - 02/22/2019 : 12:46:59 AM
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Hi,
The fitting function body has a limitation of characters around 6000, and the limitation of parameter number is 277.
However, Origin should not crash even your function exceed character limitation. there should be error message to notify user the limitation. We will see whether we can improve this.
Echo
OriginLab Technical Service |
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Nonlinear Curve fitting - equation crashes origin