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arXiv · 2311.08541

Three invariants of geometrically vertex decomposable ideals

Thai Thanh Nguyen·Jenna Rajchgot·Adam Van Tuyl
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Abstract

We study three invariants of geometrically vertex decomposable ideals: the Castelnuovo-Mumford regularity, the multiplicity, and the $a$-invariant. We show that these invariants can be computed recursively using the ideals that appear in the geometric vertex decomposition process. As an application, we prove that the $a$-invariant of a geometrically vertex decomposable ideal is non-positive. We also recover some previously known results in the literature including a formula for the regularity of the Stanley--Reisner ideal of a pure vertex decomposable simplicial complex, and proofs that some well-known families of ideals are Hilbertian. Finally, we apply our recursions to the study of toric ideals of bipartite graphs. Included among our results on this topic is a new proof for a known bound on the $a$-invariant of a toric ideal of a bipartite graph.

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Thai Thanh Nguyen, Jenna Rajchgot, Adam Van Tuyl. 2023-11-14. Three invariants of geometrically vertex decomposable ideals. https://doi.org/10.2140/pjm.2024.333.357

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