How to get the same filtered results from signal processing tool box using functions?

Hi, I have a question about filtering using MATLAB.

this is my data

readtable('data.csv')

ans = 541×1 table
     Var1 
    ______

    59.332
    58.728
    57.993
    57.118
    55.805
    54.072
    52.431
    51.219
    50.026
     48.35
    46.418
    44.741
    43.431
    42.304
    41.223
     40.18

And I wish to apply Savitzky-Golay filter using

sgolayfilt()

and get the same results from the same filtering in Signal Processing Toolbox (which are much smoother) .

However, when I tried, I get following results

filtered data using sgolayfilt(data, 3, 11) above

filtered data using signal processing tool box with all options 'auto'

I wish to know how toget below figure without using the toolbox.

Is there any way?

Thank you.

[Jan]

When I load your data, I get a different signal:

It looks like you have posted a cropped signal here. Then an exact omparsion is hard. Please post the data you are actually working with.

With sgolayfilt(data, 3, 51) the output looks like your screenshot (except for the cropping).

Answer 1

[Joe Vinciguerra]

To see what the Signal Analyzer is doing under the hood to your data, click the "Analyzer" tab and select "Generate Function". Smoothing the data with the Savitzky-Golay method and otherwise "default" settings should produce the following output when you generate the function:

function y = preprocess(x)
%  Preprocess input x
%    This function expects an input vector x.

% Generated by MATLAB(R) 9.12 and Signal Processing Toolbox 9.0.
% Generated on: 23-Aug-2022 15:27:06

y = smoothdata(x,'sgolay');

You can see here that Signal Analyzer isn't directly calling the sgolayfilt function, but the smoothdata function with the sgolay method and default parameters (default degree = 2, window is determined heuristically). Check out the help page for more details.