2014/10/27 by Zhenjie Ren, Ren, Zhenjie, Nizar Touzi +3 · 1 citation
Economics, Econometrics and Finance · Mathematics · #35D40 #35K10 #60H10 #60H30 #Analysis of PDEs (math.AP) #Economic theories and models #FOS: Mathematics #Mathematical Biology Tumor Growth #Probability (math.PR) #Stochastic processes and financial applications
paper · pdf · doi:10.48550/arxiv.1410.7281
openalex publication_date 2014/10/27 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
This paper provides a probabilistic proof of the comparison result for viscosity solutions of path-dependent semilinear PDEs. We consider the notion of viscosity solutions introduced in \citeEKTZ which considers as test functions all those smooth processes which are tangent in mean. When restricted to the Markovian case, this definition induces a larger set of test functions, and reduces to the notion of stochastic viscosity solutions analyzed in \citeBayraktarSirbu1,BayraktarSirbu2. Our main result takes advantage of this enlargement of the test functions, and provides an easier proof of comparison. This is most remarkable in the context of the linear path-dependent heat equation. As a key ingredient for our methodology, we introduce a notion of punctual differentiation, similar to the corresponding concept in the standard viscosity solutions \citeCaffarelliCabre, and we prove that semimartingales are almost everywhere punctually differentiable. This smoothness result can be viewed as the counterpart of the Aleksandroff smoothness result for convex functions. A similar comparison result was established earlier in \citeEKTZ. The result of this paper is more general and, more importantly, the arguments that we develop do not rely on any representation of the solution.