question about the signal smoothing example


I have a question about the signal smoothing example given in the documentation of Matlab.

load bostemp

days = (1:31*24)/24;
plot(days, tempC)
axis tight
ylabel('Temp (\circC)')
xlabel('Time elapsed from Jan 1, 2011 (days)')
title('Logan Airport Dry Bulb Temperature (source: NOAA)')

I understand that this example wants to emphasize that the measurements are taken 24 hours a day, 31 days for January. So the variable ‘days’ ranges from 1 to 31*24. But why divide it by 24?


hoursPerDay = 24;
coeff24hMA = ones(1, hoursPerDay)/hoursPerDay;
avg24hTempC = filter(coeff24hMA, 1, tempC);
plot(days,[tempC avg24hTempC])

I understand that this example refers to the moving average of length N (in this case N = 24). I don’t understand why there is a need to set N = 24. Why can’t it be just N = 1?

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For the first question, the data is recorded hourly, so the samples are done in 1:31*24. However, in the display, the x axis is labeled as days, that’s why it needs to be divided by 24.

For the second question, the N is basically the window length you use to smooth the data…..




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