Supermartingale shadow couplings: the decreasing case

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Publication:6178554

DOI10.3150/23-BEJ1592arXiv2207.11732OpenAlexW4388514237MaRDI QIDQ6178554

Dominykas Norgilas, Shuoqing Deng, Erhan Bayraktar

Publication date: 16 January 2024

Published in: Bernoulli (Search for Journal in Brave)

Abstract: For two measures mu and u that are in convex-decreasing order, Nutz and Stebegg (Canonical supermartingale couplings, Ann. Probab., 46(6):3351--3398, 2018) studied the optimal transport problem with supermartingale constraints and introduced two canonical couplings, namely the increasing and decreasing transport plans, that are optimal for a large class of cost functions. In the present paper we provide an explicit construction of the decreasing coupling piD by establishing a Brenier-type result: (a generalised version of) piD concentrates on the graphs of two functions. Our construction is based on the concept of the supermartingale extit{shadow} measure and requires a suitable extension of the results by Juillet (Stability of the shadow projection and the left-curtain coupling, Ann. Inst. H. Poincar'e Probab. Statist., 52(4):1823--1843, November 2016) and Beiglb"ock and Juillet (Shadow couplings, Trans. Amer. Math. Soc., 374:4973--5002, 2021) established in the martingale setting. In particular, we prove the stability of the supermartingale shadow measure with respect to initial and target measures mu,u, introduce an infinite family of lifted supermartingale couplings that arise via shadow measure, and show how to explicitly determine the `martingale points' of each such coupling.


Full work available at URL: https://arxiv.org/abs/2207.11732





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