Create a time series process based on a supplied ts.model.
gen_model(N, theta, desc, objdesc)An interger containing the amount of observations for the time series.
A vec containing the parameters to use to generate the model
A vector<string> containing the different model types (AR1, WN, etc..)
A field<vec> contains the different model objects e.g. AR1 = c(1,1)
A vec that contains combined time series.