(a) Define stopping time of a game. Let τ be the stopping time of a game. Then show that
(i) n=1,2, ... τ = n in S(n) n=1,2, ... x(n)x(n) = Y(1) + Y(2) + ... + Y(n). P(Y(n) = 1) = P(Y(n) = -1) = 1/2. Z(n) = (-1)^n cos(πx(n)) A(n) = σ(Y(1), Y(2), ..., Y(n))
I. (a) Define stopping time of a game. Let τ be the stopping time of a game. Then show that (i) and (ii) are equivalent, for each n = 1, 2, ... (b) Let X be a symmetric random walk, that is X + X = X where {Yn}n∈N is a sequence of i.i.d. random variables such that 1
show that Zn = (-1)^n cos(πXn) is a martingale with respect to F = (Y1, Y2, ..., Y)