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 Curve fitting: Breit-wigner-fano line		  New Topic  Reply to Topic
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jakefilik

UK
1 Posts
Posted - 01/17/2002 :  02:50:27 AM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
Hello, i'm very new to origin and am having a few troubles. I am trying to curve fit with a Breit wigner fano line, only after messing round for a few hours, manual in hand, i realise i have no idea what im doing!
the equation is: y = {y0[1+2(x-xc)/Qw]^2}/{1+[2(x-xc)/w]^2}
the curve is a skewed loretzian where Q is the skewness factor.
If anyone has any tips that would be great.

easwar

USA
1965 Posts
Posted - 01/17/2002 :  5:17:19 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hello,

Please take a look at this tech review article:
http://www.originlab.com/www/resources/tech_reviews/may98/topic1p1.asp

Also, if you have 6.x, you can look at the sample project located at:
\Sample Projects\Data Analysis\Curve Fitting\NLSF User Def Func
under your Origin installation directory.

You can find help on such topics by searching the knowledge base:
http://www.originlab.com/www/support/techdataform.asp

The upcoming version of Origin, ver 7, will provide a built-in C compiler that will make fitting with user-defined functions much faster than it is currently in ver 6.x
For more information on what is new in ver 7.0, please take a look at:
http://www.originlab.com/www/products/origin7/index.asp

Easwar
OriginLab.



Edited by - easwar on 01/17/2002 17:19:56
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vccer

Malaysia
4 Posts
Posted - 01/22/2002 :  10:08:23 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hello,

I am trying on BWF fitting on Origin 5 too,
y=(y0* (1 + 2*(x - xc)/(Q*F))^ 2)/ (1 + (2*(x - xc)/F)^2) + (a + b*x)
works for 1 curve fit; but it doesn't support multiple peaks.
Appreciate if anyone can help out on the multiple peaks fit. Will the newer version of origin help?

Thanks,
SS
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rtoomey

USA
184 Posts
Posted - 01/25/2002 :  10:10:34 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Replicas are designed to work with built-in functions only (not user-defined). To duplicate this replica feature, you should create your function so that it duplicates itself. For instance, if you define the equation using the EQUATIONS form, you can then enter something like:

peak1 = (y0*(1 + 2*(x - xc1)/(Q1*F1))^ 2)/ (1 + (2*(x - xc1)/F1)^2) + (a1 + b1*x);
peak2 = (y0*(1 + 2*(x - xc2)/(Q2*F2))^ 2)/ (1 + (2*(x - xc2)/F2)^2) + (a2 + b2*x);
y = peak1 + peak2;

You would then need to define both sets of parameters in the Parameter Names field and initialize them separately. If you find this taxing, the best this to do would be to set up initial parameter values in Scripts => Initializations. This menu is accessible in the advanced mode of the fitter. To get there, click on the More button in the bottom right corner of the fitter window. If you see a Basic Mode button there instead, you are already in the advanced mode.

As Easwar said, Origin 7.0 will make this much faster. You could even define this function in Origin C so that it is available at all times.

Hope this helps.

- rtoomey
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