Dual attainment for the martingale transport problem

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Publication:2419652

DOI10.3150/17-BEJ1015zbMATH Open1470.49071arXiv1705.04273OpenAlexW2962893500MaRDI QIDQ2419652

Jan Obłój, Tongseok Lim, Mathias Beiglböck

Publication date: 14 June 2019

Published in: Bernoulli (Search for Journal in Brave)

Abstract: We investigate existence of dual optimizers in one-dimensional martingale optimal transport problems. While [BNT16] established such existence for weak (quasi-sure) duality, [BHP13] showed existence for the natural stronger pointwise duality may fail even in regular cases. We establish that (pointwise) dual maximizers exist when ymapstoc(x,y) is convex, or equivalent to a convex function. It follows that when marginals are compactly supported, the existence holds when the cost c(x,y) is twice continuously differentiable in y. Further, this may not be improved as we give examples with c(x,cdot)inC2epsilon, epsilon>0, where dual attainment fails. Finally, when measures are compactly supported, we show that dual optimizers are Lipschitz if c is Lipschitz.


Full work available at URL: https://arxiv.org/abs/1705.04273





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