A lattice path model for the volume of the Monge polytope
Abstract
Monge matrices arise throughout combinatorial optimization and algorithm design; the Monge polytope ℳpq is the set of p × q Monge matrices lying inside the standard simplex on the set of matrix coordinates. We find a Stanley decomposition of the associated affine semigroup, and use it to obtain a volume formula for ℳpq expressed as a sum over "Z-avoiding" Delannoy paths in a p × q grid. An efficient dynamic-programming implementation of this formula computes the volume in dimensions far beyond the reach of general-purpose exact-volume algorithms (e.g., the volume of ℳ20,20, which has dimension 399, is computed in a fraction of a second). As a corollary of our Stanley decomposition, we also obtain a combinatorial closed form for the Ehrhart series of ℳpq.
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BibTeX
@misc{erickson2026lattice,
title = {{A lattice path model for the volume of the Monge polytope}},
author = {William Q. Erickson and Nicholas B. Jones},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.09508},
eprint = {2609.09508},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.09508},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A lattice path model for the volume of the Monge polytope
AU - William Q. Erickson
AU - Nicholas B. Jones
PY - 2026
DA - 2026/09/08
PB - arXiv
DO - 10.48550/arxiv.2609.09508
UR - https://arxiv.org/abs/2609.09508
AB - Monge matrices arise throughout combinatorial optimization and algorithm design; the Monge polytope ℳ_pq is the set of p × q Monge matrices lying inside the standard simplex on the set of matrix coordinates. We find a Stanley decomposition of the associated affine semigroup, and use it to obtain a volume formula for ℳ_pq expressed as a sum over "Z-avoiding" Delannoy paths in a p × q grid. An efficient dynamic-programming implementation of this formula computes the volume in dimensions far beyond the reach of general-purpose exact-volume algorithms (e.g., the volume of ℳ_20,20, which has dimension 399, is computed in a fraction of a second). As a corollary of our Stanley decomposition, we also obtain a combinatorial closed form for the Ehrhart series of ℳ_pq.
ER -