smoothing function :smoothECG = sgolayfilt​(ECG_data,​7,21);

Dear all.

I saw this smoothing function applied in the peak analysis page: https://uk.mathworks.com/help/signal/examples/peak-analysis.html?searchHighlight=smooth%207%2C21&s_tid=doc_srchtitle

There is a smoothing used to remove the noisy signal. smoothECG = sgolayfilt(ECG_data,7,21);

Could any one know the (7,21) means? From the explanation, it might be referring to Savitzky-Golay filtering, but I can't find out why (7,21).

Thank you

Luqian