How to fit a base(excluding the peak) of a curve and subtract the fitted base with its corresponding unfitted curve

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Ankit Gupta
Ankit Gupta 2015-9-28
评论： dpb 2015-9-29
Hi all,
I am trying to fit a base of a curve(excluding peak form data point 10:22) using a polynomial expression, I want to programmatically fit the base line (excluding peak) and do the subtraction of the fitted and unfitted data.
Is there a way to fit just the base and exclude the peak data points(from 10:22)?
single datasets is attached.
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Ankit Gupta
Ankit Gupta 2015-9-29
编辑：Ankit Gupta 2015-9-29
This is the raw single dataset, I just wanna fit the baseline excluding the peak data point form 10:22 Mat file contains "Tabs" as ydata and freq as xdata
Matfile link
dpb
dpb 2015-9-29
Despite the structure in the "baseline" outside the peak, without further information on the system you can't realistically fit much more than a linear baseline value in the region of the peak itself. When you use the polynomial of high order, there's not telling what it'll do in that region.

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回答（2 个）

Image Analyst
Image Analyst 2015-9-28
You forgot to attach the data. But anyway, maybe this: http://www.mathworks.com/matlabcentral/fileexchange/38841-matlab-implementation-of-harmonic-analysis-of-time-series--hants-
Or you can certainly extract everything except elements 10 to 22 and pass them into interp1(), polyfit(), or fitlm() and get a polynomial everywhere, even over the missing data points.
dpb
dpb 2015-9-28
But despite not having the data set for viewing/testing, sure...
ix=[1:9 23:length(x)]; % include points
b=polyfit(x(ix),y(ix),2); % fit second order baseline
ysub=y-polyval(b,x); % subtract baseline over entire range
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