Hi,
You can structure your loop this way to iterate over the cutoff frequencies and calculate the root mean square error:
fcutlow = (4:0.1:20); % Cut-off frequency in Hz. Start at 4 Hz, increment by 0.1 Hz and end at 20 Hz.
N = numel(fcutlow); % Number of cut-off frequencies
rmse = zeros(1,N); % Initialize the RMSE array to zeros
fs = 800; % Sampling frequency.
order = 4;
for i = 1:N
% Filter design.
[b, a] = butter(order,fcutlow(i)/(fs/2));
% Filter data.
filt = filtfilt(b,a,rawdata);
% Calculate the RMSE
rmse(i) = sqrt(mean((rawdata-filt) .^2));
end
% Plot the RMSE versus the cut-off frequency
plot(fcutlow,rmse)
xlabel('Cut-off Frequency (Hz)')
ylabel('RMSE')
