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Mathematics > Optimization and Control

arXiv:2108.04382 (math)
[Submitted on 9 Aug 2021 (v1), last revised 3 Feb 2022 (this version, v2)]

Title:The projection onto the cross

Authors:Heinz H. Bauschke, Manish Krishan Lal, Xianfu Wang
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Abstract:We consider the set of pairs of orthogonal vectors in Hilbert space, which is also called the cross because it is the union of the horizontal and vertical axes in the Euclidean plane when the underlying space is the real line. Crosses, which are nonconvex sets, play a significant role in various branches of nonsmooth analysis such as feasibility problems and optimization problems.
In this work, we study crosses and show that in infinite-dimensional settings, they are never weakly (sequentially) closed. Nonetheless, crosses do turn out to be proximinal (i.e., they always admit projections) and we provide explicit formulas for the projection onto the cross in all cases.
Subjects: Optimization and Control (math.OC); Functional Analysis (math.FA); Numerical Analysis (math.NA)
MSC classes: 41A50, 90C26 (Primary) 46C05, 90C33 (Secondary)
Cite as: arXiv:2108.04382 [math.OC]
  (or arXiv:2108.04382v2 [math.OC] for this version)
  https://doi.org/10.48550/arXiv.2108.04382

Submission history

From: Manish Krishan Lal [view email]
[v1] Mon, 9 Aug 2021 23:17:16 UTC (16 KB)
[v2] Thu, 3 Feb 2022 02:38:39 UTC (17 KB)
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