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G.Adderley
UK
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 Posted - 02/11/2008 : 07:01:49 AM
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Origin Version (Select Help-->About Origin): Pro 8
Operating System: XP
Hi
I am an Origin newbie and I am trying to fit a non linear surface equation of the form z=a*(x^b)*(y^c) where x,y,z are the variables and a,b,c are the parameters to fit. This function is not built into the non-linear surface fitting library so I have attempted to create a user function but being a newbie I have become a bit unstuck.
I have entered the equation in the user equation dialogue but am not sure what else I need to do. Would anybody be able to assit me with this?
Thanks
Geoff |
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snowli
USA
1426 Posts |
Posted - 02/11/2008 : 4:33:28 PM
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Hello Geoff,
In Origin 8, user can use Fitting Function Organizer to define and edit fitting functions. Fit is done in NLFit.
Here are detailed steps:
Choose Tools: Fitting Function Organizer.
Highlight Surface Fitting category on the left panel.
Click New Function button.
Now you can create your own fitting function.
E.g.
Function name: myfunc
Set Independent variables: x, y
Dependent Variable: z
Parameters: a, b, c
Function: z=a*(x^b)*(y^c)
You can creat your own parameter initialization code, etc.
Click Save button.
--> The function will be saved under User Files Folder\fitfunc\myfunc.fdf.
Now you can fit your data.
If your data are in XYZ column form in workbook, right click z column and Set it as Z. Highlight z column and choose Analysis: Fitting: Non-linear Surface Fit.
Find your function.
Go to Parameters tab to give initial values of a,b,c.
Click Fit button to fit. (there is also 1-Iter button to do step by step fit, and Fit till converge button).
Fitted surface will be put to a Matrix.
Fit result will be put to a result sheet next to source data sheet.
Note: If your source data in Matrix window of Origin, you can do surface fit as well.
Thanks, Snow Li
OriginLab Corp.
Edited by - snowli on 02/11/2008 4:34:26 PM |
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G.Adderley
UK
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Posted - 02/12/2008 : 08:12:00 AM
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Thanks Snow Li
It worked a treat! |
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3D Surface fitting to user equation