Abstract
We study the regularity and the algebraic properties of certain lattice ideals. We establish a map \(I \mapsto \tilde I\) between the family of graded lattice ideals in an ℕ-graded polynomial ring over a field K and the family of graded lattice ideals in a polynomial ring with the standard grading. This map is shown to preserve the complete intersection property and the regularity of I but not the degree. We relate the Hilbert series and the generators of I and \(\tilde I\). If dim(I) = 1, we relate the degrees of I and \(\tilde I\). It is shown that the regularity of certain lattice ideals is additive in a certain sense. Then, we give some applications. For finite fields, we give a formula for the regularity of the vanishing ideal of a degenerate torus in terms of the Frobenius number of a semigroup. We construct vanishing ideals, over finite fields,with prescribed regularity and degree of a certain type. Let X be a subset of a projective space over a field K. It is shown that the vanishing ideal of X is a lattice ideal of dimension 1 if and only if X is a finite subgroup of a projective torus. For finite fields, it is shown that X is a subgroup of a projective torus if and only if X is parameterized by monomials. We express the regularity of the vanishing ideal over a bipartite graph in terms of the regularities of the vanishing ideals of the blocks of the graph.
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Dedicated to Aron Simis on the occasion of his 70th birthday.
The first author was partially funded by CMUC and FCT (Portugal), through European program COMPETE/FEDER and project PTDC/MAT/111332/2009, and by a research grant from Santander Totta Bank (Portugal).
The second author is amember of the Center forMathematicalAnalysis,Geometry, andDynamical Systems, Departamento de Matematica, Instituto Superior Tecnico, 1049-001 Lisboa, Portugal. The third author was partially supported by SNI.
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Neves, J., Pinto, M.V. & Villarreal, R.H. Regularity and algebraic properties of certain lattice ideals. Bull Braz Math Soc, New Series 45, 777–806 (2014). https://doi.org/10.1007/s00574-014-0075-5
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DOI: https://doi.org/10.1007/s00574-014-0075-5