Question regarding the smooth filter function when using the Savitzky-Golay method

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Alberto Paredes
Alberto Paredes 2021-8-17
回答： Star Strider 2021-8-19
When using the following line of code what is my polynomial order and frame width for my Savitzky-Golay filter? What are these default settings?
Y = smoothdata(X,'sgolay');

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回答（2 个）

Jan
Jan 2021-8-19
According to the documentation, the degree can be determined and the window size is replied as 2nd output:
% SMOOTHDATA(...,'sgolay',...,'Degree',D) specifies the degree for the
% Savitzky-Golay filter.
% [B, WINSIZE] = SMOOTHDATA(...) also returns the moving window length.
You can set a breakpoint in the code of smoothdata to see, how the parameters are determined. In Matlab R2018b this line would be my point to start:
[dim,method,winsz,nanflag,t,sgdeg,dvars] = parseInputs(A, varargin{:});
Star Strider
Star Strider 2021-8-19
From the documentation:
‘... a fixed window length that is determined heuristically’
This can be returned as the second output from smoothdata if requested.
and for 'Degree' (see Smoothing Options):
‘The value of 'Degree' corresponds to the degree of the polynomial in the Savitzky-Golay filter that fits the data within each window, which is 2 by default.’
(I prefer 'Degree',3, so I always specify it.)

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