4.4. (Exponential martingales) Suppose 0(t, w) = (01(t, w),...,0n(t, w)) e R" with Ok(t,w) E V[0, T] for k = 1,..., n, where T <∞. Define Zi = exp 0(s,w)dB(s) – 0
4.4. (Exponential martingales) Suppose 0(t, w) = (01(t, w),...,0n(t, w)) e R" with Ok(t,w) E V[0, T] for k = 1,..., n, where T <∞. Define Zi = exp 0(s,w)dB(s) – 0
Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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Question
exponential martingale stochastic diff equation problem
![4.4. (Exponential martingales)
Suppose 0(t, w) = (01(t, w),...,0n(t, w)) e R" with Ok(t,w) E V[0, T]
for k = 1,..., n, where T <∞. Define
Zi = exp
0(s,w)dB(s) –
0<t<T
where B(s) E R" and 0² = 0 · 0 (dot product).
a) Use Itô's formula to prove that
dZ; = Z,0(t, w)dB(t) .
b) Deduce that Z; is a martingale for t < T, provided that
Z,0r(t, w) E V[0, T]
for 1<k< n.
Remark. A sufficient condition that Z, be a martingale is the Kazamaki
condition
E exp ( / 0(s, w)dB(s)
for all t<T.
(4.3.9)
This is implied by the following (stronger) Novikov condition
E exp
i, w)ds
(4.3.10)
See e.g. Ikeda & Watanabe (1989), Section III.5, and the references
therein.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F4f84e8f7-b971-450c-a485-c719bf1153d8%2Fed52e512-c94e-4641-bc32-9290243bc28c%2Fxxp4akd_processed.png&w=3840&q=75)
Transcribed Image Text:4.4. (Exponential martingales)
Suppose 0(t, w) = (01(t, w),...,0n(t, w)) e R" with Ok(t,w) E V[0, T]
for k = 1,..., n, where T <∞. Define
Zi = exp
0(s,w)dB(s) –
0<t<T
where B(s) E R" and 0² = 0 · 0 (dot product).
a) Use Itô's formula to prove that
dZ; = Z,0(t, w)dB(t) .
b) Deduce that Z; is a martingale for t < T, provided that
Z,0r(t, w) E V[0, T]
for 1<k< n.
Remark. A sufficient condition that Z, be a martingale is the Kazamaki
condition
E exp ( / 0(s, w)dB(s)
for all t<T.
(4.3.9)
This is implied by the following (stronger) Novikov condition
E exp
i, w)ds
(4.3.10)
See e.g. Ikeda & Watanabe (1989), Section III.5, and the references
therein.
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