# 2-25-09
?polyroot
# 1-phi1*x-phi2*x^2
phi1=1.38;phi2=-0.74
z=c(1,-phi1,-phi2)
Mod(polyroot(z))
# all magnitude of the roots >1, so stationarity
abs(phi2)  #?<1
phi2+phi1   #?<1
phi2-phi1   #?<1