关键词 > PSTAT174/274
PSTAT 174/274: Assignment # 1
发布时间:2023-02-19
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
PSTAT 174/274: Assignment # 1.
(Released 13th Feb - Due 18th Feb 11:55pm PST)
• All Questions are equally weighted and this worksheet contributes 15% to overall grade. (if included in best 2 out of 3)
• To get full marks you must show all working and justify your solution/discussion or interpret your solution where appropriate.
• If the question is a code question you must comment all code appropriately and present all outputs with correct labelling of plots and discussion/captions.
1. (174 & 274 attempt) Gaussian White Noise and its square .
(Total marks for question 33%)
Find out whether each of the following processes {Xt} is weakly stationary or nonstationary. For the weakly stationary processes, find the mean and autocovariance functions. Consider in each question that {ϵt} ∼ WN (0, σ2 ).
i (Total marks for sub-question 8.25%)
Xt = µ + ϵt for some finite constant µ ∈ R.
ii (Total marks for sub-question 8.25%)
Xt = cos (ω (t − ϕ)) + ϵt for fixed constants ω and ϕ .
iii (Total marks for sub-question 8.25%)
X1 = { 0(1 with)ot(p)h(r)is(bi)liety p
and Xt = Xt − 1 for t ≥ 2.
iv (Total marks for sub-question 8.25%)
X0 = 0, and Xt = Xt − 1 + ϵt for t ≥ 1. Hint: note here that ϵt must be independent of Xt − 1 .
2. (174 & 274 attempt) Properties of Stationarity.
(Total marks for question 33%)
i (Total marks for sub-question 16.5%)
Let {Zt} be Gaussian white noise, i.e. {Zt} is a sequence of i.i.d. normal r.v.s each with mean zero
and variance 1. Define
Xt = { 1 − 1)/^2, i(i)f(f) t(t) i(i)s(s) o(e)d(v)d(en);
Show that {Xt} is WN(0, 1) (that is, variables Xt and Xt+k, k ≥ 1, are uncorrelated with mean zero and variance 1) but that Xt and Xt − 1 are not i.i.d.
ii (Total marks for sub-question 16.5%)
If {Xt} and {Yt} are uncorrelated stationary sequences, i.e., if Xr and Ys are uncorrelated for every r and s, show that {Xt + Yt} is stationary with autocovariance function equal to the sum of the autocovariance functions of {Xt} and {Yt}.
3. (174 & 274 attempt) Time Series Models with Trend Structures.
(Total marks for question 33%)
Questions:
i (Total marks for sub-question 16.5%)
Let Xt = Zt + θZt − 1 , t = 1, 2, . . ., where Zt ∼ IID(0, σZ(2)). Show that Xt is both weakly and strictly stationary.
ii (Total marks for sub-question 16.5%)
Suppose that (Yt) is a (weakly) stationary process. Show that the process,
Xt = β0 + β1 t + Yt ,
is not stationary, but the process Zt = ∇Xt is weakly stationary.