# Produces chart like Chart B in G E P Box and G M Jenkins, Time Series
# Analysis: Forecasting and Control, San Francisco: Holden-Day 1970 and 1976.
# 
par(col=1)
plot(0,type="n",xlim=c(-2,2),xlab="phi1 (=2*rho)",ylim=c(-1,1),ylab="phi2",
     axes=T)
for (i in 1:21) segments(-2+(i-1)/5,-1,0,1,col=3)
par(col=2)
for (i in 1:20) {
  k <- -1+(i-1)/10
  par(new=T)
  curve(0.5*((k+1)-sqrt(k^2-2*k+1+4*x^2)),xlim=c(-2,2),xlab="",
  ylim=c(-1,1),ylab="",axes=F)
}