Ehrhart positivity for lattice path matroids
Pith reviewed 2026-05-22 03:58 UTC · model grok-4.3
The pith
All lattice path matroids are Ehrhart positive.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We prove that all lattice path matroids are Ehrhart positive. This unifies and generalizes numerous results on the Ehrhart positivity of matroids developed over the last two decades. We rely on our previous work on the positivity of order polynomials of fences. Our main result supports the conjecture on the Ehrhart positivity of positroids. Furthermore, our main result implies that all Schubert matroids are Ehrhart positive, which thus settles a conjecture, and supports a conjecture on the Ehrhart positivity of Schubitopes.
What carries the argument
The transfer of positivity from order polynomials of fences to the Ehrhart polynomials of lattice path matroids.
If this is right
- Many separate earlier proofs for specific matroid families now follow as special cases.
- All Schubert matroids are Ehrhart positive.
- The result supports the conjecture that positroids are Ehrhart positive.
- The result supports the conjecture that Schubitopes are Ehrhart positive.
Where Pith is reading between the lines
- The same reduction might work for other natural families of matroids once their order polynomials are understood.
- Explicit Ehrhart polynomial formulas for small lattice path matroids could be checked directly to test the pattern.
- Links between fence order polynomials and other combinatorial counting functions may yield further positivity results.
Load-bearing premise
Positivity of the order polynomials of fences holds and carries over to the Ehrhart setting for lattice path matroids.
What would settle it
A concrete lattice path matroid whose Ehrhart polynomial has a negative coefficient.
Figures
read the original abstract
We prove that all lattice path matroids are Ehrhart positive. This unifies and generalizes numerous results on the Ehrhart positivity of matroids developed over the last two decades. We rely on our previous work on the positivity of order polynomials of fences. Our main result supports the conjecture by Ferroni, Jochemko, and Schr\"oter (2022) on the Ehrhart positivity of positroids. Furthermore, our main result implies that all Schubert matroids are Ehrhart positive, which thus settles a conjecture by Fan and Li (2024), and supports a conjecture by Monical, Tokcan, and Yong (2019) on the Ehrhart positivity of Schubitopes.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proves that all lattice path matroids are Ehrhart positive. It establishes an algebraic reduction showing that the Ehrhart polynomial of any lattice path matroid equals, up to a simple shift, the order polynomial of an associated fence poset; positivity then follows from the authors' prior result on the positivity of order polynomials for all fences. The result unifies and generalizes two decades of work on matroid Ehrhart positivity, implies Ehrhart positivity for all Schubert matroids (settling a conjecture of Fan and Li), and supports conjectures of Ferroni-Jochemko-Schröter on positroids and of Monical-Tokcan-Yong on Schubitopes.
Significance. If the reduction holds, the result is a substantial advance: it supplies a uniform, algebraic proof for a broad and natural class of matroids rather than case-by-case arguments. The explicit connection between matroid Ehrhart polynomials and fence order polynomials is a technical strength, as is the fact that the argument is exact rather than asymptotic. The implications for the three cited conjectures further increase the paper's impact within combinatorial Ehrhart theory and matroid combinatorics.
minor comments (4)
- [§3] The precise construction of the fence poset from a given lattice path matroid (Definition 3.1 and the statement of Theorem 3.4) would benefit from an additional sentence clarifying how the rank function of the matroid determines the fence heights.
- [Theorem 3.4] In the proof of the main reduction (Theorem 3.4), the shift relating the Ehrhart and order polynomials is stated but not written out explicitly; adding the exact formula would make the positivity transfer immediate to the reader.
- [Introduction] The introduction's summary of prior Ehrhart-positivity results for specific matroid classes could list the exact classes covered by each cited paper to make the unification claim easier to verify.
- Notation for the fence poset (e.g., the use of F(G) versus F(M)) is consistent but could be collected in a short notation table or paragraph to aid readers unfamiliar with the authors' earlier fence work.
Simulated Author's Rebuttal
We thank the referee for the positive evaluation of our manuscript, the recognition of its unifying algebraic approach via reduction to fence order polynomials, and the recommendation for minor revision. We are pleased that the implications for the conjectures of Ferroni-Jochemko-Schröter, Fan-Li, and Monical-Tokcan-Yong have been noted as strengthening the paper's impact.
Circularity Check
No significant circularity; reduction to prior result is independent
full rationale
The manuscript establishes a self-contained algebraic reduction equating the Ehrhart polynomial of a lattice path matroid (up to shift) with the order polynomial of an associated fence poset. Positivity then follows from the authors' earlier theorem on fence order polynomials, which is a separate, externally verifiable statement about posets rather than a re-derivation or fit internal to this paper. No step in the present derivation reduces by construction to its own inputs, renames a known result, or relies on a uniqueness claim imported from the same authors' prior work to force the conclusion. The self-citation is ordinary mathematical dependence on a previously proven theorem and does not create circularity.
Axiom & Free-Parameter Ledger
axioms (1)
- standard math Standard definitions and properties of matroids, lattice path matroids, Ehrhart polynomials, and order polynomials of posets hold as in the combinatorial literature.
Reference graph
Works this paper leans on
-
[1]
Fomin, Sergey and Kirillov, Anatol N. , TITLE =. J. Algebraic Combin. , FJOURNAL =. 1997 , NUMBER =. doi:10.1023/A:1008694825493 , URL =
-
[2]
Skew shapes, Ehrhart positivity and beyond. arXiv e-prints , keywords =. doi:10.48550/arXiv.2503.16403 , archivePrefix =. 2503.16403 , primaryClass =
-
[3]
Liu, Fu and Tsuchiya, Akiyoshi , TITLE =. Adv. in Appl. Math. , FJOURNAL =. 2019 , PAGES =. doi:10.1016/j.aam.2019.03.004 , URL =
-
[4]
Morier-Genoud, Sophie and Ovsienko, Valentin , TITLE =. Forum Math. Sigma , FJOURNAL =. 2020 , PAGES =. doi:10.1017/fms.2020.9 , URL =
-
[5]
Matroids are not. Adv. Math. , FJOURNAL =. 2022 , PAGES =. doi:10.1016/j.aim.2022.108337 , URL =
-
[6]
Padrol, Arnau and Pilaud, Vincent and Ritter, Julian , TITLE =. Int. Math. Res. Not. IMRN , FJOURNAL =. 2023 , NUMBER =. doi:10.1093/imrn/rnac042 , URL =
-
[7]
Rank polynomials of fence posets are unimodal , JOURNAL =
Kantarc. Rank polynomials of fence posets are unimodal , JOURNAL =. 2023 , NUMBER =. doi:10.1016/j.disc.2022.113218 , URL =
-
[8]
Hibi, Takayuki and Higashitani, Akihiro and Tsuchiya, Akiyoshi and Yoshida, Koutarou , TITLE =. Graphs Combin. , FJOURNAL =. 2019 , NUMBER =. doi:10.1007/s00373-018-1990-9 , URL =
-
[9]
Order Polytopes of Dimension $\leq 13$ are Ehrhart Positive
Order Polytopes of Dimension 13 are Ehrhart Positive. arXiv e-prints , keywords =. doi:10.48550/arXiv.2412.07164 , archivePrefix =. 2412.07164 , primaryClass =
work page internal anchor Pith review Pith/arXiv arXiv doi:10.48550/arxiv.2412.07164
- [10]
-
[11]
Recent trends in algebraic combinatorics , SERIES =
Liu, Fu , TITLE =. Recent trends in algebraic combinatorics , SERIES =. 2019 , MRCLASS =. doi:10.1007/978-3-030-05141-9\_6 , URL =
-
[12]
McMullen, P. , TITLE =. Proc. London Math. Soc. (3) , FJOURNAL =. 1977 , NUMBER =. doi:10.1112/plms/s3-35.1.113 , URL =
-
[13]
Beck, Matthias and Robins, Sinai , TITLE =. 2015 , PAGES =. doi:10.1007/978-1-4939-2969-6 , URL =
-
[14]
Ehrhart, Eug\`. Sur les poly\`. C. R. Acad. Sci. Paris , FJOURNAL =. 1962 , PAGES =
work page 1962
- [15]
-
[16]
Fink, Alex and M\'esz\'aros, Karola and St. Dizier, Avery , TITLE =. Adv. Math. , FJOURNAL =. 2018 , PAGES =. doi:10.1016/j.aim.2018.05.028 , URL =
-
[17]
Fan, Neil J. Y. and Guo, Peter L. , TITLE =. J. Combin. Theory Ser. A , FJOURNAL =. 2021 , PAGES =. doi:10.1016/j.jcta.2020.105311 , URL =
-
[18]
Monical, Cara and Tokcan, Neriman and Yong, Alexander , TITLE =. Selecta Math. (N.S.) , FJOURNAL =. 2019 , NUMBER =. doi:10.1007/s00029-019-0513-8 , URL =
- [19]
-
[20]
The polytope of all matroids. arXiv e-prints , keywords =. doi:10.48550/arXiv.2502.20157 , archivePrefix =. 2502.20157 , primaryClass =
- [21]
-
[22]
SIAM Journal on Discrete Mathematics , volume=
Effective poset inequalities , author=. SIAM Journal on Discrete Mathematics , volume=. 2023 , publisher=
work page 2023
-
[23]
A New Approach to Order Polynomials of Labeled Posets and Their Generalizations , author=. 2003 , eprint=
work page 2003
-
[24]
Generalized permutahedra: Minkowski linear functionals and Ehrhart positivity , author=. Mathematika , volume=. 2022 , publisher=
work page 2022
-
[25]
Kahane, Yakob , title =
-
[26]
Kreweras, G. , year=. Sur une classe de problèmes de dénombrement liés au treillis des partitions des entiers , journal=
-
[27]
Speyer, David and Williams, Lauren K. , TITLE =. Trans. Amer. Math. Soc. Ser. B , FJOURNAL =. 2021 , PAGES =. doi:10.1090/btran/67 , URL =
-
[28]
Fink, Alex and Rinc\'on, Felipe , TITLE =. J. Combin. Theory Ser. A , FJOURNAL =. 2015 , PAGES =. doi:10.1016/j.jcta.2015.06.001 , URL =
- [29]
- [30]
-
[31]
Castillo, Federico and Liu, Fu , TITLE =. Discrete Comput. Geom. , FJOURNAL =. 2018 , NUMBER =. doi:10.1007/s00454-017-9950-3 , URL =
-
[32]
Castillo, Federico and Liu, Fu , TITLE =. Algebr. Comb. , FJOURNAL =. 2021 , NUMBER =. doi:10.5802/alco.157 , URL =
-
[33]
Jochemko, Katharina and Ravichandran, Mohan , TITLE =. Mathematika , FJOURNAL =. 2022 , NUMBER =. doi:10.1112/mtk.12122 , URL =
-
[34]
Stanley, Richard P. , TITLE =. Discrete Comput. Geom. , FJOURNAL =. 1986 , NUMBER =. doi:10.1007/BF02187680 , URL =
-
[35]
Ferroni, Luis , title =. Comb. Theory , issn =. 2023 , language =. doi:10.5070/C63362796 , keywords =
-
[36]
The unimodality of the Ehrhart $\delta$-polynomial of the chain polytope of the zig-zag poset
The unimodality of the Ehrhart -polynomial of the chain polytope of the zig-zag poset. arXiv e-prints , keywords =. doi:10.48550/arXiv.1603.08283 , archivePrefix =. 1603.08283 , primaryClass =
work page internal anchor Pith review Pith/arXiv arXiv doi:10.48550/arxiv.1603.08283
-
[37]
Kirillov, Anatol N. , TITLE =. Physics and combinatorics 1999 (. 2001 , ISBN =. doi:10.1142/9789812810199\_0006 , URL =
-
[38]
Coons, Jane Ivy and Sullivant, Seth , TITLE =. Electron. J. Combin. , FJOURNAL =. 2023 , NUMBER =. doi:10.37236/11526 , URL =
-
[39]
McGinnis, Daniel , TITLE =. J. Comb. , FJOURNAL =. 2025 , NUMBER =. doi:10.4310/joc.241216210956 , URL =
-
[40]
Bonin, Joseph and de Mier, Anna and Noy, Marc , TITLE =. J. Combin. Theory Ser. A , FJOURNAL =. 2003 , NUMBER =. doi:10.1016/S0097-3165(03)00122-5 , URL =
-
[41]
The geometry of geometries: matroid theory, old and new , BOOKTITLE =. [2023] 2023 , ISBN =
work page 2023
-
[42]
Kalai, Gil , TITLE =. I. [2023] 2023 , ISBN =. doi:10.4171/ICM2022/211 , URL =
-
[43]
Eur, Christopher , TITLE =. Bull. Amer. Math. Soc. (N.S.) , FJOURNAL =. 2024 , NUMBER =. doi:10.1090/bull/1803 , URL =
-
[44]
Derksen, Harm and Fink, Alex , TITLE =. Adv. Math. , FJOURNAL =. 2010 , NUMBER =. doi:10.1016/j.aim.2010.04.016 , URL =
-
[45]
Valuations for matroid polytope subdivisions , JOURNAL =
Ardila, Federico and Fink, Alex and Rinc\'. Valuations for matroid polytope subdivisions , JOURNAL =. 2010 , NUMBER =. doi:10.4153/CJM-2010-064-9 , URL =
-
[46]
Bonin, Joseph E. and de Mier, Anna , TITLE =. European J. Combin. , FJOURNAL =. 2006 , NUMBER =. doi:10.1016/j.ejc.2005.01.008 , URL =
- [47]
-
[48]
Lam, Thomas and Postnikov, Alexander , TITLE =. Forum Math. Sigma , FJOURNAL =. 2024 , PAGES =. doi:10.1017/fms.2024.11 , URL =
-
[49]
Chen, Yiming and Li, Yao and Yao, Ming , TITLE =. Proc. Amer. Math. Soc. , FJOURNAL =. 2026 , NUMBER =. doi:10.1090/proc/17525 , URL =
-
[50]
Deligeorgaki, Danai and McGinnis, Daniel and Vindas-Mel\'endez, Andr\'es R. , TITLE =. SIAM J. Discrete Math. , FJOURNAL =. 2026 , NUMBER =. doi:10.1137/25M1738103 , URL =
-
[51]
Knauer, Kolja and Mart\'inez-Sandoval, Leonardo and Ram\'irez Alfons\'in, Jorge Luis , TITLE =. Discrete Comput. Geom. , FJOURNAL =. 2018 , NUMBER =. doi:10.1007/s00454-018-9965-4 , URL =
-
[52]
Kyle and Zhuang, Yan , TITLE =
Petersen, T. Kyle and Zhuang, Yan , TITLE =. European J. Combin. , FJOURNAL =. 2025 , PAGES =. doi:10.1016/j.ejc.2024.104073 , URL =
-
[53]
Oxford Univer- sity Press (2018).https://doi.org/10.1093/oso/9780198814788.001.0001
Oxley, James , TITLE =. 2011 , PAGES =. doi:10.1093/acprof:oso/9780198566946.001.0001 , URL =
work page doi:10.1093/acprof:oso/9780198566946.001.0001 2011
-
[54]
McConville, Thomas and Sagan, Bruce E. and Smyth, Clifford , TITLE =. Discrete Math. , FJOURNAL =. 2021 , NUMBER =. doi:10.1016/j.disc.2021.112483 , URL =
-
[55]
Ehrhart polynomials of rank two matroids , JOURNAL =
Ferroni, Luis and Jochemko, Katharina and Schr\". Ehrhart polynomials of rank two matroids , JOURNAL =. 2022 , PAGES =. doi:10.1016/j.aam.2022.102410 , URL =
-
[56]
Postnikov, Alexander , TITLE =. Int. Math. Res. Not. IMRN , FJOURNAL =. 2009 , NUMBER =. doi:10.1093/imrn/rnn153 , URL =
- [58]
-
[59]
Eur, Christopher and Huh, June and Larson, Matt , TITLE =. Forum Math. Pi , FJOURNAL =. 2023 , PAGES =. doi:10.1017/fmp.2023.24 , URL =
-
[60]
Ferroni, Luis and Schr\"oter, Benjamin , TITLE =. J. Lond. Math. Soc. (2) , FJOURNAL =. 2024 , NUMBER =. doi:10.1112/jlms.12984 , URL =
-
[61]
On lattice path matroid polytopes: alcoved triangulations and snake decompositions. arXiv e-prints , keywords =. doi:10.48550/arXiv.2303.10458 , archivePrefix =. 2303.10458 , primaryClass =
-
[62]
Ehrhart polynomials of matroid polytopes and polymatroids , JOURNAL =
De Loera, Jes\'. Ehrhart polynomials of matroid polytopes and polymatroids , JOURNAL =. 2009 , NUMBER =. doi:10.1007/s00454-008-9080-z , URL =
-
[63]
Ferroni, Luis , TITLE =. Discrete Comput. Geom. , FJOURNAL =. 2022 , NUMBER =. doi:10.1007/s00454-021-00313-4 , URL =
-
[64]
Lascoux, Alain and Sch. Polyn. C. R. Acad. Sci., Paris, S. 1982 , Language =
work page 1982
- [65]
-
[66]
Macdonald, I. G. , note =
-
[67]
Knauer, Kolja and Mart\'inez-Sandoval, Leonardo and Ram\'irez Alfons\'in, Jorge Luis , TITLE =. Adv. in Appl. Math. , FJOURNAL =. 2018 , PAGES =. doi:10.1016/j.aam.2016.11.008 , URL =
-
[68]
Fan, Neil J. Y. and Li, Yao , TITLE =. Discrete Comput. Geom. , FJOURNAL =. 2024 , NUMBER =. doi:10.1007/s00454-023-00495-z , URL =
-
[69]
and McGinnis, Daniel and Miyata, Dane and Nasr, George D
Hanely, Derek and Martin, Jeremy L. and McGinnis, Daniel and Miyata, Dane and Nasr, George D. and Vindas-Mel\'endez, Andr\'es R. and Yin, Mei , TITLE =. Adv. Geom. , FJOURNAL =. 2023 , NUMBER =. doi:10.1515/advgeom-2023-0020 , URL =
-
[70]
Macdonald, I. G. , TITLE =. Surveys in combinatorics, 1991 (. 1991 , ISBN =
work page 1991
-
[71]
Gessel, Ira M. and Krattenthaler, C. , Title =. Trans. Am. Math. Soc. , ISSN =. 1997 , DOI =
work page 1997
-
[72]
Tableau formula for vexillary double Edelman--Greene coefficients , author=. 2024 , eprint=
work page 2024
-
[73]
Hopkins, Sam and Lai, Tri , Title =. J. Comb. Theory, Ser. A , ISSN =. 2021 , DOI =
work page 2021
- [74]
- [75]
-
[76]
Hoffman, P. N. and Humphreys, J. F. , Title =. 1992 , Publisher =
work page 1992
-
[77]
Okada, Soichi , Title =. J. Comb. Theory, Ser. A , ISSN =. 1989 , DOI =
work page 1989
- [78]
-
[79]
Chan, Swee Hong and Pak, Igor and Panova, Greta , Title =. Trans. Am. Math. Soc. , ISSN =. 2022 , DOI =
work page 2022
-
[80]
Linial, Nathan , Title =. SIAM J. Comput. , ISSN =. 1984 , Language =. doi:10.1137/0213049 , Keywords =
-
[81]
Kung, Joseph P. S. and Rota, Gian-Carlo and Yan, Catherine H. , title =. 2009 , publisher =
work page 2009
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.