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kemeyer
39 Posts |
 Posted - 07/15/2010 : 4:30:02 PM
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Origin Ver. and Service Release (Select Help-->About Origin):8.1 SR1
Operating System:Vista
I have a question regarding the capabilities of the nlbegin/nlfit/nlend x-functions.
Basically, I have a dataset of index(n) vs wavelength(lambda) that I initially fit to the sellmeier equation:
n = sqrt(A + B*Lambda^2/(Lambda^2-C) +
D*Lambda^2/(Lambda^2-E))
Where n is the dependent variable and Lambda is the independent. I've created a user-defined function for it and was able to fit the data using the analysis>>Non-linear fit>>new dialog option from Origin's menus. After this fit, I get parameters A, B, C, D, and E.
What I want to do is use these parameters for the next step, which is finding the parameter alpha in the equation:
n = sqrt(A + B*Lambda^2/(Lambda^2-C)(1+alpha*(T-23)) +
D*Lambda^2/(Lambda^2-E)(1+alpha*(T-23)))
Where I have the data of Temperature (T) vs. index(n) at a given wavelength(lambda).I know they need to be fixed, but I am unsure of how to go about doing this. Should I assign nltree:= to the output of the first fitting? One problem I see is that in the second equation, Lambda is a constant (but a different one for each data set I am looking at). Here, the independent variable is T, the dependent is still n, and the parameter is alpha (A, B, C, D, E, and Lambda will all be fixed).
Do you have any suggestions or pertinent examples I could look at? I searched the wiki page for Origin but I didn't see anything that clarified or answered my questions.
I'd really appreciate any help you could give me,
Katie
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VincentLiu
China
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Posted - 07/16/2010 : 05:27:23 AM
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The following is an example to show you how to fix the parameter xc of the gauss function at 5.
nlbegin iy:=(1,2) func:=gauss nltree:=ParamTree;
ParamTree.xc = 5; // Assign an initial value 5 to xc
ParamTree.f_xc = 1; // Add the prefix "f_" before xc and assign 1 to "f_xc" to fix xc
nlfit;
nlend;
You can click here to get another example to show you how to fix parameters and then unfix them.
vincent
OriginLab Technical Services
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Edited by - VincentLiu on 07/16/2010 05:28:43 AM |
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nlbegin/nlfit/nlend