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(a) For the ARMA(1,2) model Yt=0.8Yt−1+et+0.7et−1+0.6et−2, show that: (i) ρk=0.8ρk−1 for k>2; and (ii) ρ2=0.8ρ1
Posted: Thu Jul 14, 2022 4:51 pm
by answerhappygod
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(a) For the ARMA(1,2) model Yt=0.8Yt−1+et+0.7et−1+0.6et−2, show that: (i) ρk=0.8ρk−1 for k>2; and (ii) ρ2=0.8ρ1+0.6/γ0. (b) Let Yt be an AR(2) process of the special form Yt=ϕ2Yt−2+et. (i) Find the range of values of ϕ2 for which the process is stationary. (ii) Show that if ∣ϕ2∣=1 the process cannot be stationary.