FITTING WITH TWO FUNCTION AT ONE TIME?

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Thu, 07/29/2010 - 05:34 am

Hi,

I'm pretty new to Igor and I think I have no talent in coding at all...... So pls help.

my question like this, I have set of intensity I(q) and q data , what I want to so is fit the data to a new function which composed of powerlaw and gaussian function. see attached file. where the I0 is the peak height, q0 is the mean postion, B is the width of the peak.
is there sb can let me know how can I do this in Igor?


 data.pxp
amyAUS wrote:
amy one can help,Please.......thanks


(assuming your data are already loaded as Iwave and qwave)


  • open the Analysis:Curve Fitting menu

  • select Iwave as the y data and qwave as the x data

  • click on New Fit Function

  • enter a name

  • enter parameters that you want to fit --- EXAMPLE: a, b, c

  • define the independent parameter --- EXAMPLE: x

  • write the equation for your function in the space given -- EXAMPLE: f(x) = a*x + b*x^2 + c*log(x)

  • save the fit function

  • click the coefficients tab

  • provide some initial values for the coefficients

  • click the Do It button


    • HTH

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

July 29, 2010 at 10:00 am - Permalink

I used the Multipeak Fit 2 package (Analysis->Packages->Multipeak Fit 2) to fit your data. I didn't use the equation you included in your first post, which is just a power law plus a Gaussian peak. Your data are not symmetrical- it is hard to see how they would fit a Gaussian peak shape.

At any rate, I used two exponentially-modifed Gaussian peaks to fit your data. I have added a picture of the result to this post.

I should also note that I fitted a somewhat restricted portion of your data; I don't think that's important. I also used a linear background function. A constant background worked very nearly identically.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com
MultipeakFit_Set1.png

August 2, 2010 at 12:58 pm - Permalink