library(forecast)

set.seed(123)
ar1.sim<-arima.sim(model=list(ar=c(0.7)), n=100)
ar1.sim

par(mfrow=c(3,1))
ts.plot(ar1.sim)
acf(ar1.sim)
pacf(ar1.sim)

ar1<-arima(ar1.sim, order=c(1,0,0), include.mean=T)
ar1
ar2<-arima(ar1.sim, order=c(2,0,0), include.mean=T)
ar3<-arima(ar1.sim, order=c(3,0,0), include.mean=T)

AIC(ar1,ar2,ar3, k = 2)
BIC(ar1,ar2,ar3)

res<-residuals(ar1)
ts.plot(res)
acf(res)
pacf(res)

Box.test(res,lag=1, type=c("Ljung-Box"))

predict(ar1, n.ahead = 4)
(far1<-forecast(ar1, h=4))
plot(far1)