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Zur Izhakian

Publications and source records attributed to Zur Izhakian.

At least 19 recordsLinked to original sources
arXiv2026

Almost subtractive submonoids of additive monoids and related quadratic forms

We introduce and study the class of almost subtractive submonoids of additive monoids. This property relaxes the strict condition of subtractivity while still allowing for a simulated subtraction operation sufficient for many algebraic applications. We explore the structural properties of these monoids and demonstrate their significance in the theory of modules over semirings, specifically regarding quadratic forms and their companions.

math.RA↗
arXiv2024

Supertropical Monoids III: Factorization and splitting covers

The category $STROP_m$ of supertropical monoids, whose morphisms are transmissions, has the full--reflective subcategory $STROP$ of commutative semirings. In this setup, quotients are determined directly by equivalence relations, as ideals are not applicable for monoids, leading to a new approach to factorization theory. To this end, tangible factorization into irreducibles is obtained through fiber contractions and their hierarchy. Fiber contractions also provide different quotient structures, associated with covers and types of splitting covers.

math.AC↗
arXiv2023

Archimedean classes in additive monoids

Summand absorbing submodules are common in modules over (additively) idempotent semirings, for example, in tropical algebra. A submodule $W$ of $V$ is summand absorbing, if $x + y \in W$ implies $x \in W, \; y \in W $ for any $x, y \in V$. This paper proceeds the study of these submodules, and more generally of additive monoids, with emphasis on their archimedean classes and quotient structures.

math.AC↗
arXiv2022

Stratifications of the ray space of a tropical quadratic form by Cauchy-Schwartz functions

Classes of an equivalence relation on a module V over a supertropical semiring, called rays, carry the underlaying structure of "supertropical trigonometry" and thereby a version of convex geometry which is compatible with quasilinearity. In this theory the traditional Cauchy-Schwarz inequality is replaced by the CS-ratio which gives rise to special characteristic functions, called CS-functions. These functions partite the ray space Ray(V) into convex sets and establish a main tool for analyzing varieties of quasilinear stars in Ray(V). They provide stratifications of Ray(V) and therefore a finer convex analysis that helps for a better geometric understanding.

math.RA↗
arXiv2022

Subordinate quadratic forms and isometric maps over semirings

The paper expands the theory of quadratic forms on modules over a semiring R, introduced in [12]-[14], especially in the setup of tropical and supertropical algebra. Isometric linear maps induce subordination on quadratic forms, and provide a main tool in our current study. These maps allow lifts and pushdowns of quadratic forms on different modules, preserving basic characteristic properties.

math.RA↗
arXiv2020

Amalgamation and extensions of summand absorbing modules over a semiring

A submodule $W$ of $V$ is summand absorbing, if $x + y \in W$ implies $x \in W, \; y \in W $ for any $x, y \in V$. Such submodules often appear in modules over (additively) idempotent semirings, particularly in tropical algebra. This paper studies amalgamation and extensions of these submodules, and more generally of upper bound modules.

math.RA↗
arXiv2019

Cauchy-Schwarz functions and convex partitions in the ray space of a supertropical quadratic form

Rays are classes of an equivalence relation on a module V over a supertropical semiring. They provide a version of convex geometry, supported by a "supertropical trigonometry" and compatible with quasilinearity, in which the CS-ratio takes the role of the Cauchy-Schwarz inequality. CS-functions which emerge from the CS-ratio are a useful tool that helps to understand the variety of quasilinear stars in the ray space Ray(V). In particular, these functions induce a partition of Ray(V) into convex sets, and thereby a finer convex analysis which includes the notions of median, minima, glens, and polars.

math.RA↗
arXiv2019

Supertropical Monoids II: Lifts, Transmissions, and Equalizers

The category $\operatorname{STROP}$ of commutative semirings, whose morphisms are transmissions, is a full and reflective subcategory of the category $\operatorname{STROP}_m$ of supertropical monoids. Equivalence relations on supertropical monoids are constructed easily, and utilized effectively for supertropical semirings, whereas ideals are too special for semirings. Aiming for tangible factorizations, certain types of such equivalence relations are constructed and classified explicitly in this paper, followed by a profound study of their characteristic properties with special emphasis on difficulties arising from ghost products of tangible elements.

math.AC↗
arXiv2019

Commutative $ν$-algebra and supertropical algebraic geometry

This paper lays out a foundation for a theory of supertropical algebraic geometry, relying on commutative $ν$-algebra. To this end, the paper introduces $\mathfrak{q}$-congruences, carried over $ν$-semirings, whose distinguished ghost and tangible clusters allow both quotienting and localization. Utilizing these clusters, $\mathfrak{g}$-prime, $\mathfrak{g}$-radical, and maximal $\mathfrak{q}$-congruences are naturally defined, satisfying the classical relations among analogous ideals. Thus, a foundation of systematic theory of commutative $ν$-algebra is laid. In this framework, the underlying spaces for a theoretic construction of schemes are spectra of $\mathfrak{g}$-prime congruences, over which the correspondences between $\mathfrak{q}$-congruences and varieties emerge directly. Thereby, scheme theory within supertropical algebraic geometry follows the Grothendieck approach, and is applicable to polyhedral geometry.

math.AC↗
arXiv2019

Generation of summand absorbing submodules

An $R$-module $V$ over a semiring $R$ lacks zero sums (LZS) if $ x +y = 0 \; \Rightarrow \; x = y = 0$. More generally, asubmodule $W$ of $V$ is "summand absorbing", if $ \forall \, x, y \in V: \ x + y \in W \; \Rightarrow \; x \in W, \; y \in W. $ These relate to tropical algebra and modules over idempotent semirings, as well as modules over semirings of sums of squares. In previous work, we have explored the lattice of summand absorbing submodules of a given LZS module, especially those that are finitely generated, in terms of the lattice-theoretic Krull dimension. In this note we describe their explicit generation.

math.RA↗
arXiv2018

Quasilinear convexity and quasilinear stars in the ray space of a supertropical quadratic form

Relying on rays, we search for submodules of a module V over a supertropical semiring on which a given anisotropic quadratic form is quasilinear. Rays are classes of a certain equivalence relation on V, that carry a notion of convexity, which is consistent with quasilinearity. A criterion for quasilinearity is specified by a Cauchy-Schwartz ratio which paves the way to a convex geometry on Ray(V), supported by a "supertropical trigonometry". Employing a (partial) quasiordering on Ray(V), this approach allows for producing convex quasilinear sets of rays, as well as paths, containing a given quasilinear set in a systematic way. Minimal paths are endowed with a surprisingly rich combinatorial structure, delivered to the graph determined by pairs of quasilinear rays -- apparently a fundamental object in the theory of supertropical quadratic forms.

math.RA↗
arXiv2018

Semigroup identities of tropical matrices through matrix ranks

We prove the conjecture that, for any $n$, the monoid of all $n \times n$ tropical matrices satisfies nontrivial semigroup identities. To this end, we prove that the factor rank of a large enough power of a tropical matrix does not exceed the tropical rank of the original matrix.

math.RA↗
arXiv2017

Supertropical $\operatorname{SL}_n$

Extending earlier work on supertropical adjoints and applying symmetrization, we provide a symmetric supertropical version $\operatorname {SLS}_n$ of the special linear group, which we partition into submonoids, based on "quasi-identity" matrices, and we display maximal sub-semigroups of $\operatorname {SLS}_n$. We also study the monoid generated by $\operatorname {SLS}_n$. Several illustrative examples are given of unexpected behavior. We describe the action of elementary matrices on $\operatorname {SLS}_n$, which enables one to connect different matrices in $\operatorname {SLS}_n$, but in a weaker sense than the classical situation.

math.RA↗
arXiv2017

Tropical plactic algebra, the cloaktic monoid, and semigroup representations

A new tropical plactic algebra is introduced in which the Knuth relations are inferred from the underlying semiring arithmetics, encapsulating the ubiquitous plactic monoid $\mathcal{P}_n$. This algebra manifests a natural framework for accommodating representations of $\mathcal{P}_n$, or equivalently of Young tableaux, and its moderate coarsening -- the cloaktic monoid $\mathcal{K}_n$ and the co-cloaktic $ ^{\operatorname{co}}\mathcal{K}_n$. The faithful linear representations of $\mathcal{K}_n$ and $\, ^{\operatorname{co}} \mathcal{K}_n$ by tropical matrices, which constitute a tropical plactic algebra, are shown to provide linear representations of the plactic monoid. To this end the paper develops a special type of configuration tableaux, corresponding bijectively to semi-standard Young tableaux. These special tableaux allow a systematic encoding of combinatorial properties in numerical algebraic ways, including algorithmic benefits. The interplay between these algebraic-combinatorial structures establishes a profound machinery for exploring semigroup attributes, in particular satisfying of semigroup identities. This machinery is utilized here to prove that $\mathcal{K}_n$ and $\, ^{\operatorname{co}} \mathcal{K}_n$ admit all the semigroup identities satisfied by $n \times n$ triangular tropical matrices, which holds also for $\mathcal{P}_3$.

math.CO↗
arXiv2016

Pure Dimension and Projectivity of Tropical Polytopes

We study how geometric properties of tropical convex sets and polytopes, which are of interest in many application areas, manifest themselves in their algebraic structure as modules over the tropical semiring. Our main results establish a close connection between pure dimension of tropical convex sets, and projectivity (in the sense of ring theory). These results lead to a geometric understanding of idempotency for tropical matrices. As well as their direct interest, our results suggest that there is substantial scope to apply ideas and techniques from abstract algebra (in particular, ring theory) in tropical geometry.

math.RA↗
arXiv2015

Decompositions of modules lacking zero sums

A direct sum decomposition theory is developed for direct summands (and complements) of modules over a semiring $R$, having the property that $v+w = 0$ implies $v = 0$ and $w = 0$. Although this never occurs when $R$ is a ring, it always does holds for free modules over the max-plus semiring and related semirings. In such situations, the direct complement is unique, and the decomposition is unique up to refinement. Thus, every finitely generated projective module is a finite direct sum of summands of $R$ (assuming the mild assumption that $1$ is a finite sum of orthogonal primitive idempotents of $R$). Some of the results are presented more generally for weak complements and semidirect complements. We conclude by examining the obstruction to the "upper bound" property in this context.

math.RA↗
arXiv2015

Quadratic and Symmetric Bilinear Forms on Modules with Unique Base Over a Semiring

We study quadratic forms on free modules with unique base, the situation that arises in tropical algebra, and prove the analog of Witt's Cancellation Theorem. Also, the tensor product of an indecomposable bilinear module $(U, γ)$ with an indecomposable quadratic module $(V,q) $ is indecomposable, with the exception of one case, where two indecomposable components arise.

math.RA↗