On the unboundedness of martingale transforms
A martingale problem approach is used first to analyze compactness and continuous dependence of the solution set to stochastic differential inclusions of Ito type with convex integrands on the initial distributions. Next the problem of existence of optimal weak solutions to such inclusions and their dependence on the initial distributions is investigated.
Let F be a filtration andτbe a random time. Let G be the progressive enlargement of F withτ. We study the following formula, called the optional splitting formula: For any G-optional processY, there exists an F-optional processY′ and a function Y′′ defined on [0,∞] × (ℝ+ × Ω) being ℬ[0,∞]⊗x1d4aa;(F) measurable, such that Y=Y′1[0,τ)+Y′′(τ)1[τ,∞). (This formula can also be formulated for multiple random timesτ1,...,τk). We are interested in this formula because of its fundamental role in many...