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arxiv: 2606.28680 · v1 · pith:EW2OX6TRnew · submitted 2026-06-27 · 🧮 math.CO

Persistent Subdivisions of Coxeter Permutahedra

Pith reviewed 2026-06-30 10:04 UTC · model grok-4.3

classification 🧮 math.CO
keywords Coxeter permutahedramatroid polytopespersistent simplicestriangulationssubdivisionsCoxeter groupspolytope realizations
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The pith

The geometric properties of Coxeter permutahedra realized as matroid polytopes change in controlled ways as the generating vector a varies.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper studies polytopes formed as the convex hull of the orbit of a generic point a under a finite Coxeter group W. These objects are both Coxeter permutahedra and Coxeter matroid polytopes. The authors focus on tracking persistent simplices, triangulations, and subdivisions as a is varied. This investigation connects the combinatorial action of the group to the geometric structure of the polytope.

Core claim

Polytopes of the form conv(W · a) for generic a realize Coxeter permutahedra that are also Coxeter matroid polytopes, and their triangulations and subdivisions feature persistent simplices whose presence and structure depend on the choice of a in a manner that can be analyzed through the group action and matroid properties.

What carries the argument

The orbit polytope conv(W · a) for generic a, which encodes the geometric properties through the Coxeter group action and allows study of persistent features in subdivisions.

If this is right

  • Persistent simplices appear in the triangulations across different values of a.
  • The subdivisions can be described using the matroid structure associated with the polytope.
  • Changes in a lead to controlled modifications in the geometric features of the polytope.
  • The properties hold for all finite Coxeter groups acting on R^n.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • This approach could extend to classifying all matroid polytopes that admit Coxeter symmetry.
  • Computations for small groups like the symmetric group could test the persistence explicitly.
  • Links may exist to other subdivision theories in polyhedral combinatorics.

Load-bearing premise

That polytopes of the form conv(W · a) for generic a can be treated as both Coxeter permutahedra and Coxeter matroid polytopes simultaneously.

What would settle it

A counterexample where for some generic a the polytope conv(W · a) lacks the expected persistent simplices in its subdivisions would disprove the persistence claims.

Figures

Figures reproduced from arXiv: 2606.28680 by Jes\'us A. De Loera, Melissa Sherman-Bennett, Timothy Blanton.

Figure 1
Figure 1. Figure 1: Hexagons which are not (projections of) an orbit S3-permutahedron. (a) (101714,753589,861628,925275) (b) (32919, 67492, 433170, 464108) (c) (1, 5, 10) [PITH_FULL_IMAGE:figures/full_fig_p006_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: (A), (B): S4 orbit permutahedra for different choices of a. (C) A B3 orbit permutahedron. Displayed beneath each polytope is the choice of base point a. 3.2. The S4 case. Let W = S4. Then we have that B = {a ∈ R 4 | a1 < a2 < a3 < a4}. In this case, P W (a) is a 3-dimensional polytope in R 4 . From the work of Steinitz [29, 30], the realization space of the S4-permutahedron (modulo affine equivalence) is c… view at source ↗
Figure 3
Figure 3. Figure 3: The convex hull of {(1234),(2143),(3412),(4321)} · a in two different orbit per￾mutahedra. For S4, there are 278 distinct chirotopes, with the number of a-simplices ranging from 9, 780 (for the regular permutahedron) to 10, 152. For generic a (e.g. those that avoid the hypersurfaces shown in [PITH_FULL_IMAGE:figures/full_fig_p007_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Left: The plane (0, x, y, 1) with the fundamental chamber for W = S4 shaded in green. Right: The plane (1, x, y) with the fundamental chamber of W = B3 in green. Both: The fundamental chamber is subdivided according to the chirotope of P W (a). That is, all a in the same region have the same chirotope. When you move to the boundary of a region, some number of simplices collapse to coplanar sets. When you c… view at source ↗
Figure 5
Figure 5. Figure 5: The convex hull of {(1234),(1324),(2143),(3142)} · a in two different orbit per￾mutahedra. Note the simplex has negative volume in (a) and positive volume in (b). Proposition 5.8. There exist a, a ′ which are generic in the sense of Theorem 5.7, but the oriented matroids of W · a and W · a ′ differ. In particular, there is a collection {Si} of subsets of W which is a (regular) a-triangulation but not a a ′… view at source ↗
read the original abstract

We investigate the realizations of Coxeter permutahedra which are also Coxeter matroid polytopes; these are polytopes of the form $\mathrm{conv}(W \cdot \mathbf{a})$ where $W$ is a finite Coxeter group acting on $\mathbb{R}^n$ and $\mathbf{a}$ is generic. Our main focus is how the geometric properties of $\mathrm{conv}(W \cdot \mathbf{a})$ change as $\mathbf{a}$ changes, with particular attention to persistent simplices, triangulations, and subdivisions.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 1 minor

Summary. The manuscript investigates realizations of Coxeter permutahedra that are simultaneously Coxeter matroid polytopes, specifically the polytopes conv(W · a) for a finite Coxeter group W acting on R^n and generic a. The central focus is the dependence of geometric properties on the choice of a, with emphasis on persistent simplices, triangulations, and subdivisions.

Significance. If the claimed results on persistent subdivisions hold, the work would provide a systematic study of how subdivisions of these polytopes vary with the generic vector a, potentially unifying aspects of Coxeter matroid theory with subdivision theory. The setup is standard in the literature, and the introduction of persistence as a lens could open connections to other areas of combinatorial geometry.

minor comments (1)
  1. The abstract states the objects under study but does not indicate the main theorems or the precise definition of 'persistent simplices'; a clearer statement of the principal results would help readers assess the contribution.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their review and for accurately summarizing the content and potential significance of our work on persistent subdivisions of Coxeter permutahedra. No major comments were provided in the report.

Circularity Check

0 steps flagged

No significant circularity; self-contained mathematical investigation

full rationale

The paper describes an investigation of geometric properties (persistent simplices, triangulations, subdivisions) of polytopes conv(W · a) that are simultaneously Coxeter permutahedra and Coxeter matroid polytopes for generic a. This is a definitional setup in combinatorial geometry with no fitted parameters, no predictions derived from data subsets, and no load-bearing self-citations or ansatzes that reduce claims to inputs by construction. The abstract and described program contain no equations or derivations that could exhibit circularity. The central program of tracking variation with a is independent of any internal reduction.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review yields no explicit free parameters, axioms, or invented entities; the objects are defined in terms of standard Coxeter group actions and matroid polytopes from prior literature.

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Works this paper leans on

31 extracted references · 15 canonical work pages

  1. [1]

    Coxeter submodular functions and deformations of Coxeter permutahedra

    F. Ardila, F. Castillo, C. Eur, and A. Postnikov. “Coxeter submodular functions and deformations of Coxeter permutahedra”. In:Adv. Math.365 (2020), pp. 107039, 36.issn: 0001-8708,1090-2082.doi: 10.1016/j.aim.2020.107039.url:https://doi.org/10.1016/j.aim.2020.107039

  2. [2]

    A regular unimodular triangulation of the matroid base polytope

    S. Backman and G. Liu. “A regular unimodular triangulation of the matroid base polytope”. In:Duke Math. J.174.14 (2025), pp. 3047–3061.issn: 0012-7094,1547-7398.doi:10.1215/00127094- 2025- 0015.url:https://doi.org/10.1215/00127094-2025-0015

  3. [3]

    How to integrate a polynomial over a simplex

    V. Baldoni, N. Berline, J. A. De Loera, M. K¨ oppe, and M. Vergne. “How to integrate a polynomial over a simplex”. In:Math. Comp.80.273 (2011), pp. 297–325.issn: 0025-5718,1088-6842.doi: 10.1090/S0025-5718-2010-02378-6.url:https://doi.org/10.1090/S0025-5718-2010-02378- 6

  4. [4]

    Barvinok.Integer Points in Polyhedra

    A. Barvinok.Integer Points in Polyhedra. Zurich Lectures in Advanced Mathematics. Z¨ urich: European Mathematical Society, 2008.isbn: 978-3-03719-052-4

  5. [5]

    An Algorithmic Theory of Lattice Points in Polyhedra

    A. Barvinok and J. E. Pommersheim. “An Algorithmic Theory of Lattice Points in Polyhedra”. In:New Perspectives in Algebraic Combinatorics. Ed. by L. J. Billera, A. Bj¨ orner, C. Greene, R. E. Simion, and R. P. Stanley. Vol. 38. Mathematical Sciences Research Institute Publications. Cambridge: Cambridge University Press, 1999, pp. 91–147

  6. [6]

    Beck and S

    M. Beck and S. Robins.Computing the continuous discretely: integer-point enumeration in polyhedra. Undergraduate Texts in Mathematics. Springer, 2007

  7. [7]

    Bj¨ orner and F

    A. Bj¨ orner and F. Brenti.Combinatorics of Coxeter groups. Vol. 231. Graduate Texts in Mathematics. Springer, New York, 2005, pp. xiv+363.isbn: 978-3540-442387; 3-540-44238-3

  8. [8]

    Bj¨ orner, M

    A. Bj¨ orner, M. L. Vergnas, B. Sturmfels, N. White, and G. M. Ziegler.Oriented Matroids. 2nd. Vol. 46. Encyclopedia of Mathematics and its Applications. Cambridge: Cambridge University Press, 1999

  9. [9]

    A. V. Borovik, I. M. Gelfand, and N. White.Coxeter matroids. Vol. 216. Progress in Mathematics. Birkh¨ auser Boston, Inc., Boston, MA, 2003, pp. xxii+264.isbn: 0-8176-3764-8.doi:10.1007/978- 1-4612-2066-4.url:https://doi.org/10.1007/978-1-4612-2066-4. 17

  10. [10]

    Tropical flag varieties

    M. Brandt, C. Eur, and L. Zhang. “Tropical flag varieties”. In:Adv. Math.384 (2021), Paper No. 107695, 41.issn: 0001-8708,1090-2082.doi:10.1016/j.aim.2021.107695.url:https://doi.org/ 10.1016/j.aim.2021.107695

  11. [11]

    The\(s\)-Weak Order and\(s\)-Permutahedra I: Combinatorics and Lattice Structure

    C. Ceballos and V. Pons. “The\(s\)-Weak Order and\(s\)-Permutahedra I: Combinatorics and Lattice Structure”. In:SIAM J. Discret. Math.38.4 (2024), pp. 2855–2895.doi:10.1137/23M1605818.url: https://doi.org/10.1137/23m1605818

  12. [12]

    Wonderful models of subspace arrangements

    C. De Concini and C. Procesi. “Wonderful models of subspace arrangements”. In:Selecta Mathematica (N.S.)1.3 (1995), pp. 459–494.doi:10.1007/BF01589496

  13. [13]

    Ehrhart Polynomials of Matroid Polytopes and Poly- matroids

    J. A. De Loera, D. C. Haws, and M. K¨ oppe. “Ehrhart Polynomials of Matroid Polytopes and Poly- matroids”. In:Discrete & Computational Geometry42.4 (2009), pp. 670–702.doi:10.1007/s00454- 008-9080-z

  14. [14]

    J. A. De Loera, J. Rambau, and F. Santos.Triangulations. Vol. 25. Algorithms and Computation in Mathematics. Structures for algorithms and applications. Springer-Verlag, Berlin, 2010, pp. xiv+535. isbn: 978-3-642-12970-4.doi:10.1007/978-3-642-12971-1.url:https://doi.org/10.1007/978- 3-642-12971-1

  15. [15]

    Defant, M

    C. Defant, M. Sherman-Bennett, and N. Williams.Permutahedron Triangulations via Total Linear Stability and the Dual Braid Group. 2025. arXiv:2509.11497 [math.CO].url:https://arxiv.org/ abs/2509.11497

  16. [16]

    Hatcher.Algebraic topology

    A. Hatcher.Algebraic topology. Cambridge University Press, Cambridge, 2002, pp. xii+544.isbn: 0-521-79160-X; 0-521-79540-0

  17. [17]

    Permutahedra and generalized associahedra

    C. Hohlweg, C. E. Lange, and H. Thomas. “Permutahedra and generalized associahedra”. In:Advances in Mathematics226.1 (2011), pp. 608–640.issn: 0001-8708.doi:https://doi.org/10.1016/j.aim. 2010.07.005.url:https://www.sciencedirect.com/science/article/pii/S0001870810002586

  18. [18]

    J. E. Humphreys.Reflection groups and Coxeter groups. Vol. 29. Cambridge Studies in Advanced Mathematics. Cambridge University Press, Cambridge, 1990, pp. xii+204.isbn: 0-521-37510-X.doi: 10.1017/CBO9780511623646.url:https://doi.org/10.1017/CBO9780511623646

  19. [19]

    The universality theorems on the classification problem of configuration varieties and convex polytope varieties

    N. E. Mn”ev. “The universality theorems on the classification problem of configuration varieties and convex polytope varieties”. In:Topology and geometry—Rohlin Seminar. Vol. 1346. Lecture Notes in Math. Springer, Berlin, 1988, 527–544

  20. [20]

    Pons.Combinatorics of the Permutahedra, Associahedra, and Friends

    V. Pons.Combinatorics of the Permutahedra, Associahedra, and Friends. 2023.url:https://tel. archives-ouvertes.fr/tel-04390473

  21. [21]

    Faces of generalized permutohedra

    A. Postnikov, V. Reiner, and L. Williams. “Faces of generalized permutohedra”. In:Doc. Math.13 (2008), pp. 207–273.issn: 1431-0635,1431-0643

  22. [22]

    Permutohedra, associahedra, and beyond

    A. Postnikov. “Permutohedra, associahedra, and beyond”. In:Int. Math. Res. Not. IMRN6 (2009), pp. 1026–1106.issn: 1073-7928,1687-0247.doi:10.1093/imrn/rnn153.url:https://doi.org/10. 1093/imrn/rnn153

  23. [23]

    An inequality

    R. Rado. “An inequality”. In:J. London Math. Soc.27 (1952), pp. 1–6.issn: 0024-6107,1469-7750. doi:10.1112/jlms/s1-27.1.1.url:https://doi.org/10.1112/jlms/s1-27.1.1

  24. [24]

    Richter-Gebert.Realization spaces of polytopes

    J. Richter-Gebert.Realization spaces of polytopes. Vol. 1643. Lecture Notes in Mathematics. Springer- Verlag, Berlin, 1996, pp. viii+177.isbn: 3-540-61987-X

  25. [25]

    The universality theorems for oriented matroids and polytopes

    J. Richter-Gebert. “The universality theorems for oriented matroids and polytopes”. In:Discrete and Computational Geometry: Ten Years Later. Vol. 223. Contemp. Math. Amer. Math. Soc., Providence, RI, 1999, 269–292

  26. [26]

    Realization spaces of 4-polytopes are universal

    J. Richter-Gebert and G. M. Ziegler. “Realization spaces of 4-polytopes are universal”. In:Bull. Amer. Math. Soc. (N.S.)32.4 (1995), 403–412

  27. [27]

    P. H. Schoute.Analytic treatment of the polytopes regularly derived from the regular polytopes. Vol. 11. Verhandelingen der K. Akad. Wetenschappen te Amsterdam 3. First systematic study of the permu- tahedron (no explicit name yet). Amsterdam: Johannes M¨ uller, 1911, pp. 1–87

  28. [28]

    R. P. Stanley.Enumerative Combinatorics, Volume 1. 2nd. Vol. 49. Cambridge Studies in Advanced Mathematics. Cambridge: Cambridge University Press, 2012.isbn: 978-1-107-60262-5

  29. [29]

    Polyeder und Raumeinteilungen

    E. Steinitz. “Polyeder und Raumeinteilungen”. In:Encyklop¨ adie der Mathematischen Wissenschaften. Vol. 3.3AB12. Leipzig: Teubner, 1922, pp. 1–139. 18

  30. [30]

    Steinitz and H

    E. Steinitz and H. Rademacher.Vorlesungen ¨ uber die Theorie der Polyeder unter Einschluss der Elemente der Topologie. Vol. No. 41. Grundlehren der Mathematischen Wissenschaften. Reprint der 1934 Auflage. Springer-Verlag, Berlin-New York, 1976, pp. viii+351

  31. [31]

    Bruhat interval polytopes

    E. Tsukerman and L. Williams. “Bruhat interval polytopes”. In:Adv. Math.285 (2015), pp. 766–810. issn: 0001-8708,1090-2082.doi:10.1016/j.aim.2015.07.030.url:https://doi.org/10.1016/j. aim.2015.07.030