2. Let {X} be a moving average process of order q (usually written as MA(q)) defined on tЄ Z as where {et} is a white noise process with variance 1. (1) (a) Show that for any MA(1) process with B₁ 1 there exists another MA(1) pro- cess with the same autocorrelation function, and find the lag 1 moving average coefficient (say) of this process. (b) For an MA(2) process, equation (1) becomes X=&t+B₁et-1+ B2ɛt-2- (2) i. Define the backshift operator B, and write equation (2) in terms of a polyno- mial function B(B), giving a clear definition of this function. ii. Hence show that equation (2) can be written as an infinite order autoregressive process under certain conditions on B(B), clearly stating these conditions.

Big Ideas Math A Bridge To Success Algebra 1: Student Edition 2015
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Chapter4: Writing Linear Equations
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2. Let {X} be a moving average process of order q (usually written as MA(q)) defined on
tЄ Z as
where {et} is a white noise process with variance 1.
(1)
(a) Show that for any MA(1) process with B₁ 1 there exists another MA(1) pro-
cess with the same autocorrelation function, and find the lag 1 moving average
coefficient (say) of this process.
(b) For an MA(2) process, equation (1) becomes
X=&t+B₁et-1+ B2ɛt-2-
(2)
i. Define the backshift operator B, and write equation (2) in terms of a polyno-
mial function B(B), giving a clear definition of this function.
ii. Hence show that equation (2) can be written as an infinite order autoregressive
process under certain conditions on B(B), clearly stating these conditions.
Transcribed Image Text:2. Let {X} be a moving average process of order q (usually written as MA(q)) defined on tЄ Z as where {et} is a white noise process with variance 1. (1) (a) Show that for any MA(1) process with B₁ 1 there exists another MA(1) pro- cess with the same autocorrelation function, and find the lag 1 moving average coefficient (say) of this process. (b) For an MA(2) process, equation (1) becomes X=&t+B₁et-1+ B2ɛt-2- (2) i. Define the backshift operator B, and write equation (2) in terms of a polyno- mial function B(B), giving a clear definition of this function. ii. Hence show that equation (2) can be written as an infinite order autoregressive process under certain conditions on B(B), clearly stating these conditions.
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