MH 3512 – Stochastic Processes SEMESTER I HOMEWORK 2022–2023
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SEMESTER I HOMEWORK 2022–2023
MH 3512 – Stochastic Processes
Question 1
Let (Xn )n∈NО be a sequence of bounded random variables and consider the filtration (Fn )n∈NО defined by Fn := σ(X0 , X1 , . . . , Xn ), n e N0 .
Assume that for each n e N0 we have
匝 [Xn+1 │Fn] = 3Xn + 2.
Moreover, consider the process
Mn := 3-nXn + 3-n , n e N0 .
Then, the process (Mn )n∈NО is a martingale with respect to (Fn )n∈NО .
YES
NO
No answer
Question 2
Let (Xn )n∈NО be a sequence of bounded random variables and consider the filtration (Fn )n∈NО defined by Fn := σ(X0 , X1 , . . . , Xn ), n e N0 .
Moreover, let (Mn )n∈NО be an integrable Fn-adapted stochastic process with constant expectation, i.e. 匝[Mk ] = 匝[Ml ] for any k, l e N0 .
Then (Mn )n∈NО is a martingale with respect to (Fn )n∈NО .
YES
NO
No answer
Question 3
Let (Xn )n∈N be independent and identically distributed random variables satisfying
P(Xn = 1) = P(Xn = 一1) = .
Consider the stochastic process (Sn )n∈NО defined by S0 := 0 and for each n ≥ 1 by Sn := S0 + Xi .
Moreover, define
T := inf{n ≥ 0: Sn = 30}.
Then we have that 匝[ST ] = 30.
YES
NO
No answer
Question 4
Let (Xn )n∈NО be a branching process defined as in (8.1.1) in the script on page 310 with X0 = 1.
Assume that the corresponding (Yn )n∈N satisfy for each n e N
P(Yn = 0) = c0 , P(Yn = 2) = c2 ,
for constants c0 , c2 e (0, 1) satisfying c0 + c2 = 1, and that 匝[Yn] ≤ 1. Then the extinction probability of the branching process is equal to 1.
YES
NO
No answer
Question 5
Let (Xn )n∈NО be a branching process defined as in (8.1.1) in the script on page 310 which satisfies all the following:
● X0 = 1,
● One has limn→& 匝[Xn] = o.
Then its extinction probability is equal to zero.
YES
NO
No answer
Question 6
Let (Xn )n∈NО be a branching process defined as in (8.1.1) in the script on page 310 with X0 = 1.
Assume that the corresponding (Yn )n∈N satisfy
P(Yn = 0) = c0 , P(Yn = 1) = c1 , P(Yn = 2) = c2 ,
for constants c0 , c1 , c2 e (0, 1) satisfying c0 + c1 + c2 = 1 and
4c0 c2 一 (c0 + c2 )2 = 0.
Then the extinction probability of the branching processes is equal to 1.
YES
NO
No answer
Question 7
Let (Xn )n∈NО be a time-homogeneous Markov process with finite state space. Then (Xn )n∈NО admits a stationary distribution.
YES
NO
No answer
Question 8
Let (Xn )n∈NО be a time-homogeneous Markov process with state space § and denote for every state i e § its period by per(i).
Then for (Xn )n∈NО to admit a limiting probability distribution, it is necessary but not sufficient to satisfy i∈§ per(i) > 0.
YES
NO
No answer
Question 9
Let (Xn )n∈NО be a time-homogeneous Markov process with transition matrix P , and let (Yn )n∈NО be a time-homogeneous Markov process with transition
matrix . Assume that = Pn for some n e N n [2, o).
YES
NO
No answer
Question 10
Let (Xn )n∈NО be a time-homogeneous Markov process which admits a limiting probability distribution which is also a stationary distribution.
Then, at least one of the following three conditions needs to be satisfied:
● (Xn )n∈NО is recurrent;
● (Xn )n∈NО is aperiodic;
● (Xn )n∈NО is irreducible.
YES
NO
No answer
2022-10-31