y=rnorm(1000)
plot(y, type="l")
arima(y, order=c(1,0,1))
ARMAtoMA(ar=0.9,ma=0.5,lag.max=10)
ARMAtoAR(ar=0.9,ma=0.5,lag.max=10)

w=rnorm(1000)
y=filter(w,filter=c(3/2,-3/4),meth="rec")
plot(y)
acf(y)
rho=c(1,6/7,rep(0,29))
for (i in 3:31) rho[i]=3/2*rho[i-1]-3/4*rho[i-2]
points(0:30,rho)


ar=c(3/2,-3/4)
ma=0
lags=24
plot(ARMAacf(ar,ma,lags),type="h")
abline(h=0)
y=arima.sim(list(ar=ar,ma=ma),n=1000)
acf(y)
points(0:30,ARMAacf(ar,ma,30))


pacf(y)
points(1:30,ARMAacf(ar,ma,30,pacf=TRUE))