def arma_acf(ar, ma, nobs=10):
 acovf = arma_acovf(ar, ma, nobs)
 return (acovf / acovf[0])

def arma_acf ( ar , ma , nobs = 10 ) : acovf = arma_acovf ( ar , ma , nobs ) return ( acovf / acovf [ 0 ] )
theoretical autocorrelation function of an arma process parameters ar : array_like .