phi1=-.97
lag.max=20
plot(y=ARMAacf(ar=phi1,lag.max=lag.max),x=0:lag.max,type='h')
abline(h=0,col='blue')

library(TSA)
data(lynx)
?lynx
plot(lynx)
windows()
hist(lynx)
hist(log(lynx))
plot(log(lynx))
arima(log(lynx),order=c(2,0,0)) # fit an AR(2)

lag.max=60
phi1=1.38;phi2=-0.74
plot(y=ARMAacf(ar=c(phi1,phi2),lag.max=lag.max),x=0:lag.max,type='h')
abline(h=0,col='blue')
# quasi-period about 10 years

# about 11.5 cycles in the data of span =114 years
period=114/11.5
period