We study the problem of Regularized Unconstrained SubmodularMaximization (RegularizedUSM) as defined by Bodek and Feldman (Maximizing sums of non-monotone submodular and linear functions: understanding the unconstrained case, arXiv:2204.03412, 2022): given query access to a non-negative submodular function f:2N→R≥0\documentclass[12pt]{minimal}
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\begin{document}$$f:2^{{\mathcal {N}}}\rightarrow {\mathbb {R}}_{\ge 0}$$\end{document} and a linear function ℓ:2N→R\documentclass[12pt]{minimal}
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\begin{document}$$\ell :2^{{\mathcal {N}}}\rightarrow {\mathbb {R}}$$\end{document} over the same ground set N\documentclass[12pt]{minimal}
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\begin{document}$${\mathcal {N}}$$\end{document}, output a set T⊆N\documentclass[12pt]{minimal}
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\begin{document}$$T\subseteq {\mathcal {N}}$$\end{document} approximately maximizing the sum f(T)+ℓ(T)\documentclass[12pt]{minimal}
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\begin{document}$$f(T)+\ell (T)$$\end{document}. An algorithm is said to provide an (α,β)\documentclass[12pt]{minimal}
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\begin{document}$$(\alpha ,\beta )$$\end{document}-approximation for RegularizedUSM if it outputs a set T such that E[f(T)+ℓ(T)]≥maxS⊆N[α·f(S)+β·ℓ(S)]\documentclass[12pt]{minimal}
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\begin{document}$${\mathbb {E}}[f(T)+\ell (T)]\ge \max _{S\subseteq {\mathcal {N}}}[\alpha \cdot f(S)+\beta \cdot \ell (S)]$$\end{document}. We also consider the setting where S and T are constrained to be independent in a given matroid, which we refer to as Regularized ConstrainedSubmodular Maximization (RegularizedCSM). The special case of RegularizedCSM with monotone f has been extensively studied (Sviridenko et al. in Math Oper Res 42(4):1197–1218, 2017; Feldman in Algorithmica 83(3):853–878, 2021; Harshaw et al., in: International conference on machine learning, PMLR, 2634–2643, 2019), whereas we are aware of only one prior work that studies RegularizedCSM with non-monotone f (Lu et al. in Optimization 1–27, 2023), and that work constrains ℓ\documentclass[12pt]{minimal}
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\begin{document}$$\ell $$\end{document} to be non-positive. In this work, we provide improved (α,β)\documentclass[12pt]{minimal}
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\begin{document}$$(\alpha ,\beta )$$\end{document}-approximation algorithms for both RegularizedUSM and RegularizedCSM with non-monotone f. Specifically, we are the first to provide nontrivial (α,β)\documentclass[12pt]{minimal}
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\begin{document}$$(\alpha ,\beta )$$\end{document}-approximations for RegularizedCSM where the sign of ℓ\documentclass[12pt]{minimal}
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\begin{document}$$\ell $$\end{document} is unconstrained, and the α\documentclass[12pt]{minimal}
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\begin{document}$$\alpha $$\end{document} we obtain for RegularizedUSM improves over (Bodek and Feldman in Maximizing sums of non-monotone submodular and linear functions: understanding the unconstrained case, arXiv:2204.03412, 2022) for all β∈(0,1)\documentclass[12pt]{minimal}
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\begin{document}$$\beta \in (0,1)$$\end{document}. We also prove new inapproximability results for RegularizedUSM and RegularizedCSM, as well as 0.478-inapproximability for maximizing a submodular function where S and T are subject to a cardinality constraint, improving a 0.491-inapproximability result due to Oveis Gharan and Vondrak (in: Proceedings of the twenty-second annual ACM-SIAM symposium on discrete algorithms, SIAM, pp 1098–1116, 2011).
