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The Existential Theory of the Reals as a Complexity Class: A Compendium

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arxiv 2407.18006 v1 pith:QKTKVMYZ submitted 2024-07-25 cs.CC cs.CGcs.DScs.FLcs.LO

classification cs.CCcs.CGcs.DScs.FLcs.LO
keywords complexityexistsmathbbclasscompendiumtheoryexistentialpart
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

We survey the complexity class $\exists \mathbb{R}$, which captures the complexity of deciding the existential theory of the reals. The class $\exists \mathbb{R}$ has roots in two different traditions, one based on the Blum-Shub-Smale model of real computation, and the other following work by Mn\"{e}v and Shor on the universality of realization spaces of oriented matroids. Over the years the number of problems for which $\exists \mathbb{R}$ rather than NP has turned out to be the proper way of measuring their complexity has grown, particularly in the fields of computational geometry, graph drawing, game theory, and some areas in logic and algebra. $\exists \mathbb{R}$ has also started appearing in the context of machine learning, Markov decision processes, and probabilistic reasoning. We have aimed at collecting a comprehensive compendium of problems complete and hard for $\exists \mathbb{R}$, as well as a long list of open problems. The compendium is presented in the third part of our survey; a tour through the compendium and the areas it touches on makes up the second part. The first part introduces the reader to the existential theory of the reals as a complexity class, discussing its history, motivation and prospects as well as some technical aspects.

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Forward citations

Cited by 5 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Algorithms for Equilibria in Concurrent Stopping Games

    cs.GT 2026-07 accept novelty 7.0 of 10

    Approximate constrained NE existence in concurrent stopping games is EXPTIME (PSPACE-hard); XRSE constrained existence is NP-complete.

  2. Point Set Embeddability with List Constraints

    cs.CG 2026-07 accept novelty 7.0 of 10

    List-constrained point-set embeddability is poly-time or FPT for connected graphs on convex points, but NP-hard already for bi-labeled matchings (convex) and bi-labeled paths (general), with matching FPT/paraNP dichot...

  3. Toward Satisfiability Modulo Realizability

    cs.CG 2026-07 accept novelty 7.0 of 10

    The largest set of points in the plane with no empty convex hexagon and no convex heptagon has size 23, proved by a SAT-modulo-realizability solver that finds thousands of witnessing configurations.

  4. Data-Efficient Safe Policy Improvement Using Parametric Structure

    cs.AI 2025-07 conditional novelty 6.0 of 10

    Parametric SPIBB and game-based pruning reduce the data required for safe policy improvement by up to two orders of magnitude, while SMT-based pruning is shown to be computationally infeasible.

  5. Some structural complexity results for $\exists\mathbb R$

    cs.CC 2025-02 conditional novelty 6.0 of 10

    This paper proves oracle, logical, and Ladner-type structural theorems for the complexity class ∃R, some conditional on ∃R being different from NP.

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