'Returns the discretized `TransferFunction` system.
Parameters: See `cont2discrete` for details.
Returns
sys: instance of `dlti` and `StateSpace`'

def to_discrete(self, dt, method='zoh', alpha=None):

    return TransferFunction(dt=dt, *cont2discrete((self.num, self.den), dt, method=method, alpha=alpha)[:(-1)])
