Is there a version of Girsanov theorem when the volatility is changing?
For example Girsanov theorem states that Radon Nikodym (RN) derivative for a stochastic equation is used to transform the expectation where the sampling is done in one mesaure to an expectation where sampling is done in another measure.
Let's see an example
dXt(w)=f(Xt(w))dt+σ(Xt(w))dWPt(w) in P measure.
In P* measure, drift is f∗(Xt(w)). We multiply the internals of expectation in P measure with RN derivative to get expectation of X in P* measure
EP∗[X]=EP[XdP∗dP]
where
dP∗dP=e−0.5∫(f∗(Xs(w))−f(Xs(w))σ(Xs(w)))2ds+∫f∗(Xs(w))−f(Xs(w))σ(Xs(w))dWPs(w)
What I am looking for is in P* measure, not only drift but also the volatility changes
dXt(w)=f∗(Xt(w))dt+σ∗(Xt(w))dWPt(w)
Then what is dP∗dP?
No comments:
Post a Comment