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

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');

Answer 1

[Jan]

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{:});

Answer 2

[Star Strider]

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.)