How to determine the order of a set of data? (AR coefficient)

Hello, I am trying to use the Matlab function pyulear. Therefore, I need to determine the order of my set of data. How can I do this? I was thinking of using the function n4sid, but it does not work at all.

My code:

m = n4sid(Signal, 1:10);

order = idpoly(m)

[X, Y] = pyulear(Signal,order,length(Signal),Fs);