Construction and plotting of ARIMA model

Hello everyone,

I would like to ask some information about the construction and plotting of an ARIMA model.

I have a timeseries, inserted in matlab's workspace, named TSeries. What I want to do is to create an autoregressive model and fit it to my timeseries, since the latter has a lot of spikes during the whole time period. That's why I want someone who knows about ARIMA models to tell me if I'm doing it right.

Firstly, I define a model (of degree 1):

Md1 = arima(1,0,0);

and I estimate its parameters:

EstMd1 = estimate(Md1, Tseries);

And finally, I simulate and plot it by the next code:

Ysim1 = simulate(EstMd1, numObs);
pn1 = plot(time,    Ysim1);

However, I struggle a bit with the parameter numObs , since I cannot understand what exactly it is. Do I have to set the size of my table TSeries as the parameter numbObs ?

Thank you in advance.

Best regards, Dimitris V. Psychas