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| Main Authors: | , |
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| Format: | Preprint |
| Published: |
2024
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2408.12756 |
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| _version_ | 1866915631382659072 |
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| author | Jojić, Duško Papaz, Ognjen |
| author_facet | Jojić, Duško Papaz, Ognjen |
| contents | We show that the combinatorial types of the links of the vertices in the edgewise triangulation $T_{k,q}$ of a $(k-1)$-simplex are encoded by the partitions of $k$. Each of these complexes is isomorphic to a subcomplex of the barycentric subdivision of the boundary of a $(k-1)$-simplex, and the containment relations among them are described by a new poset on the set of partitions of $k$. We compute the $h$-vectors of these complexes and determine the number of vertices of $T_{k,q}$ whose links are the same (correspond to the same partition).
The combinatorial type of the link of an $(s-1)$-dimensional face of $T_{k,q}$ corresponds to a partition $(λ_1,λ_2,\ldots,λ_s)$ of $k$ into $s$ parts, together with additional partitions of each $λ_i$. We also enumerate the combinatorial types of all $m$-dimensional complexes that arise as the links in edgewise triangulations.
A new permutation statistic, \textit{the faithful initial part}, is introduced and used to describe the star cluster of a facet of $T_{k,q}$. By examining a specific shelling of this star cluster, we prove that the $i$-th entry of its $h$-vector
counts the number of permutations of $[k]$ with exactly $i$ descents,
taking into account the
faithful initial part as the multiplicity. Finally, we
describe a concrete shelling order for $T_{k,q}$, give a
combinatorial interpretation of its $h$-vector, and derive an explicit formula for it. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2408_12756 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Shelling of links and star clusters in edgewise subdivision of a simplex Jojić, Duško Papaz, Ognjen Combinatorics We show that the combinatorial types of the links of the vertices in the edgewise triangulation $T_{k,q}$ of a $(k-1)$-simplex are encoded by the partitions of $k$. Each of these complexes is isomorphic to a subcomplex of the barycentric subdivision of the boundary of a $(k-1)$-simplex, and the containment relations among them are described by a new poset on the set of partitions of $k$. We compute the $h$-vectors of these complexes and determine the number of vertices of $T_{k,q}$ whose links are the same (correspond to the same partition). The combinatorial type of the link of an $(s-1)$-dimensional face of $T_{k,q}$ corresponds to a partition $(λ_1,λ_2,\ldots,λ_s)$ of $k$ into $s$ parts, together with additional partitions of each $λ_i$. We also enumerate the combinatorial types of all $m$-dimensional complexes that arise as the links in edgewise triangulations. A new permutation statistic, \textit{the faithful initial part}, is introduced and used to describe the star cluster of a facet of $T_{k,q}$. By examining a specific shelling of this star cluster, we prove that the $i$-th entry of its $h$-vector counts the number of permutations of $[k]$ with exactly $i$ descents, taking into account the faithful initial part as the multiplicity. Finally, we describe a concrete shelling order for $T_{k,q}$, give a combinatorial interpretation of its $h$-vector, and derive an explicit formula for it. |
| title | Shelling of links and star clusters in edgewise subdivision of a simplex |
| topic | Combinatorics |
| url | https://arxiv.org/abs/2408.12756 |