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Jan Snellman

Publications and source records attributed to Jan Snellman.

30 records · Page 2Linked to original sources
arXiv2002

Simplicial complexes associated to certain subsets of natural numbers and its applications to multiplicative functions

We call a set of positive integers closed under taking unitary divisors a unitary ideal. It can be regarded as a simplicial complex. Moreover, a multiplicative arithmetical function on such a set corresponds to a function on the simplicial complex with the property that the value on a face is the product of the values at the vertices of that face. We use this observation to solve the following problems: 1) Let r be a positive integer and c a real number. What is the maximum value that \sum_{s \in S}g(s) can obtain when S is a unitary ideal containing precisely r prime powers, and g is the multiplicative function determined by g(s)=c when s \in S is a prime power? 2) Suppose that g is a multiplicative function which is \ge 1, and that we want to find the maximum of g(i) when 1 \le i \le n. At how many integers do we need to evaluate g?

math.CO↗
arXiv2002

Bounds for the Entropy of Graded Algebras

Newman, Schneider and Shalev defined the entropy of a graded associative algebra A as H(A) = \limsup_{n \to \infty} \sqrt[n]{a_n}, where a_n is the vector space dimension of the n'th homogeneous component. When A is the homogeneous quotient of a finitely generated free associative algebra, they showed that H(A) \le \sqrt{a_2}. Using some results of Friedland on the maximal spectral radius of 0-1 matrices with a prescribed number of ones, we improve on this bound.

math.RA↗
arXiv2002

The ring of arithmetical functions with unitary convolution: the [n]-truncation

We study a certain truncation of the ring of arithmetical functions with unitary convolution, consisting of functions vanishing on arguments >n. The truncations are artinian monomial quotients of a polynomial ring in finitely many indeterminates, and are isomorphic to the ``artinified'' Stanley-Reisner rings of certain simplicial complexes.

math.AC↗
arXiv2002

The ring of arithmetical functions with unitary convolution: General Truncations

Let A denote the ring of arithmetical functions with unitary convolution, and let V be a finite subset of the positive integers having the property that for every v in V, all unitary divisors of v lie in V. We study the truncation A_V, an artinian monomial quotient of a polynomial ring in finitely many indeterminates, isomorphic to the ``Artinified'' Stanley-Reisner ring C[\bar{Δ(V)}] of a certain simplicial complex Δ(V).

math.AC↗
arXiv2002

The ring of arithmetical functions with unitary convolution: Divisorial and topological properties

We study the ring of arithmetical functions with unitary convolution, giving an isomorphism to a generalized power series ring on infinitely many variables, similar to the isomorphism of Cashwell-Everett between the ring of arithmetical functions with Dirichlet convolution and the power series ring on countably many variables. We topologize it with respect to a natural norm, and shove that all ideals are quasi-finite. Some elementary results on factorization into atoms are obtained. We prove the existence of an abundance of non-associate regular non-units.

math.AC↗
arXiv2002

A poset classifying non-commutative term orders

We study a certain poset on the free monoid on a countable alphabet. This poset is determined by the fact that its total extensions are precisely the standard term orders. We also investigate the poset classifying degree-compatible standard term orders, and the poset classifying sorted term orders. For the latter poset, we give a Galois coconnection with the Young lattice.

math.CO↗
arXiv2001

Factorisation in Topological Monoids

The aim of this paper is sketch a theory of divisibility and factorisation in topological monoids, where finite products are replaced by convergent products. The algebraic case can then be viewed as the special case of discretely topologised topological monoids. In particular, we define the topological factorisation monoid, a generalisation of the factorisation monoid for algebraic monoids, and show that it is always topologically factorial: any element can be uniquely written as a convergent product of irreducible elements. We give some sufficient conditions for a topological monoid to be topologically factorial.

math.GN↗
arXiv2000

Lifting Grobner bases from the exterior algebra

In the article "Non-commutative Grobner bases for commutative algebras", Eisenbud-Peeva-Sturmfels proved a number of results regarding Grobner bases and initial ideals of those ideals in the free associative algebra which contain the commutator ideal. We prove similar results for ideals which contains the anti-commutator ideal (the defining ideal of the exterior algebra). We define one notion of generic initial ideals in the free assoicative algebra, and show that gin's of ideals containing the commutator ideal, or the anti-commutator ideal, are finitely generated.

math.AC↗
arXiv2000

On some partial orders associated to generic initial ideals

We study two partial orders on $[x_1,...,x_n]$, the free abelian monoid on ${x_1,...,x_n}$. These partial orders, which we call the ``strongly stable'' and the ``stable'' partial order, are defined by the property that their filters are precisely the strongly stable and the stable monoid ideals. These ideals arise in the study of generic initial ideals.

math.CO↗
arXiv2000

Generalised Hilbert Numerators II

We associate to each $r$-multigraded, locally finitely generated ideal in the "large polynomial ring" on countably many indeterminates a power series in $r$ variables; this power series is the limit in the adic topology of the numerators of the rational functions which give the Hilbert series of the truncations of the ideal. We characterise the set of all power series so obtained. Our main technical tools are an approximation result which asserts that truncation and the forming of initial ideals commute in a filtered sense, and standard inclusion/exclusion, Möbius inversion, and LCM-lattice homology methods generalised to monomial ideals in countably many variables.

math.AC↗
arXiv2000

Truncations of the ring of number-theoretic functions

We study the ring of all functions from the positive integers to some field. This ring, which we call \emph{the ring of number-theoretic functions}, is an inverse limit of the ``truncations'' Γ_n consisting of all functions f for which f(m)=0 whenever m > n. Each Γ_n is a zero-dimensional, finitely generated (K)-algebra, which may be expressed as the quotient of a finitely generated polynomial ring with a \emph{reversely stable} monomial ideal. Using the description of the free minimal resolution of stable ideals, given by Eliahou-Kervaire, and some additional arguments by Aramova-Herzog and Peeva, we give the Poincaré-Betti series for Γ_n.

math.AC↗