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The operator splitting schemes revisited: primal-dual gap and degeneracy reduction by a unified analysis

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Abstract

We revisit the operator splitting schemes proposed in a recent work of [Some extensions of the operator splitting schemes based on Lagrangian and primal-dual: A unified proximal point analysis, Feng Xue, Optimization, 2022, doi: 10.1080/02331934.2022.2057309], and further analyze the convergence of the generalized Bregman distance and the primal-dual gap of these algorithms within a unified proximal point framework. The possibility of reduction to a simple resolvent is also discussed by exploiting the structure and possible degeneracy of the underlying metric.

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Notes

  1. We say a convex function f is proximable, if the proximity operator of f has a closed-form representation or at least can be solved efficiently up to high precision [17]. This property is also called ‘simple’ [17] or ‘with inexpensive proximity operator’ [36].

  2. Note that the well-known proximal forward-backward splitting (PFBS) algorithm may not in general be applied to solve (1), since neither f nor g is assumed to be differentiable with a Lipschitz continuous gradient.

  3. For any pair of \(({\textbf{c}},{\textbf{c}}^{\prime })\), the quantity of \(\Pi ({\textbf{c}},{\textbf{c}}^{\prime })\) is generally only a difference, but not a distance, since it is not guaranteed to be non-negative.

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Acknowledgements

I am gratefully indebted to the anonymous reviewers and the editor for helpful discussions, particularly related to the convergence analysis of PPA (Lemma 1), the notion of infimal postcomposition (Lemma 2), the generalized Bregman distance and primal-dual gap (Sects. 3.3, 3.44.2 and 5.2 ), and for bringing references [34, 37, 47] to my attention.

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Xue, F. The operator splitting schemes revisited: primal-dual gap and degeneracy reduction by a unified analysis. Optim Lett 18, 155–194 (2024). https://doi.org/10.1007/s11590-023-01983-0

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