non negative least squares fitting in igor

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Dear all,

I have 3 set of measured values Y (wave0,wave1,wave2), the x value for these three sets are the same. Now I want to use two sets to fitting the third one using least squares fitting. The fitting function is very simple, which is " fit_wave_3 = A*wave0+B*wave1", A and B is the corresponding coefficient. How do I conduct that in igor?

Thank you very much. 
Function FitTwoWaves(pw, yw, xw)
    WAVE pw, yw, xw
 
    WAVE wave0, wave1
    yw = pw[0]*wave0(xw) + pw[1]*wave1(xw)
end

Note that the assignment at the end uses round parens "()" to index wave0 and wave1. If the X scaling is set correctly on wave0 and wave1, and the values are evenly spaced in X, then if your data to fit doesn't exactly match the X ranges of wave0 and wave1, Igor will do linear interpolation to get intermediate values.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com

December 11, 2014 at 09:32 am - Permalink

johnweeks wrote: 
Function FitTwoWaves(pw, yw, xw)
    
  WAVE pw, yw, xw
 
    WAVE wave0, wave1
    yw = pw[0]*wave0(xw) + pw[1]*wave1(xw)
end

Note that the assignment at the end uses round parens "()" to index wave0 and wave1. If the X scaling is set correctly on wave0 and wave1, and the values are evenly spaced in X, then if your data to fit doesn't exactly match the X ranges of wave0 and wave1, Igor will do linear interpolation to get intermediate values.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com


Dear johnweeks,
there is no variable in that function.

December 12, 2014 at 04:44 am - Permalink

lingxiaoabc wrote:
....
there is no variable in that function.


The wave pw contains the fitting coefficients, A and B in your case.

Perhaps you might explain whether you have gone through a basic fitting tutorial, for example for a simple linear regression fit? In particular, do you understand the use of coefficient waves to carry the fitting parameters?

Or perhaps you are wanting something else in your fitting function.

--
J. J. Weimer
Chemistry / Chemical & Materials Engineering, UAHuntsville

December 12, 2014 at 10:10 am - Permalink