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arXiv Open Access 2023
Sprague-Grundy Value for Common Divisor Nim

Ryotaro Nohagi

We determine the Sprague-Grundy value for the Common Divisor Nim$_m$ (CDN$_m$ for short) for $m \in \mathbb{Z}_{\ge 1}$, which is called COMMON DIVISOR game in [ANW, Chapter 2, Exercise 8 (p.55)].

en math.CO
arXiv Open Access 2021
The Curvature of Graph Products

Oliver Knill

We show that the curvature K_(G*H)(x,y) at a point (x,y) in the strong product G*H of two arbitrary finite simple graphs is equal to the product K_G(x) K_H(y) of the curvatures.

en math.CO
CrossRef Open Access 2020
-DIVISIBILITY OF CO-DEGREES OF IRREDUCIBLE CHARACTERS

ROYA BAHRAMIAN, NEDA AHANJIDEH

For a character $\unicode[STIX]{x1D712}$ of a finite group $G$, the co-degree of $\unicode[STIX]{x1D712}$ is $\unicode[STIX]{x1D712}^{c}(1)=[G:\text{ker}\unicode[STIX]{x1D712}]/\unicode[STIX]{x1D712}(1)$. We study finite groups whose co-degrees of nonprincipal (complex) irreducible characters are divisible by a given prime $p$.

DOAJ Open Access 2020
Symmetric Fundamental Expansions to Schur Positivity

Austin Roberts

We consider families of quasisymmetric functions with the property that if a symmetric function f is a positive sum of functions in one of these families, then f is necessarily a positive sum of Schur functions. Furthermore, in each of the families studied, we give a combinatorial description of the Schur coefficients of f. We organize six such families into a poset, where functions in higher families in the poset are always positive integer sums of functions in each of the lower families.

Mathematics
DOAJ Open Access 2020
Matrix product and sum rule for Macdonald polynomials

Luigi Cantini, Jan De Gier, Michael Wheeler

We present a new, explicit sum formula for symmetric Macdonald polynomials Pλ and show that they can be written as a trace over a product of (infinite dimensional) matrices. These matrices satisfy the Zamolodchikov– Faddeev (ZF) algebra. We construct solutions of the ZF algebra from a rank-reduced version of the Yang–Baxter algebra. As a corollary, we find that the normalization of the stationary measure of the multi-species asymmetric exclusion process is a Macdonald polynomial with all variables set equal to one.

Mathematics
DOAJ Open Access 2020
Rational Shi tableaux and the skew length statistic

Robin Sulzgruber

We define two refinements of the skew length statistic on simultaneous core partitions. The first one relies on hook lengths and is used to prove a refined version of the theorem stating that the skew length is invariant under conjugation of the core. The second one is equivalent to a generalisation of Shi tableaux to the rational level of Catalan combinatorics. We prove that the rational Shi tableau is injective. Moreover we present a uniform definition of the rational Shi tableau for Weyl groups and conjecture injectivity in the general case.

Mathematics
DOAJ Open Access 2020
Continued Classification of 3D Lattice Models in the Positive Octant

Axel Bacher, Manuel Kauers, Rika Yatchak

We continue the investigations of lattice walks in the three-dimensional lattice restricted to the positive octant. We separate models which clearly have a D-finite generating function from models for which there is no reason to expect that their generating function is D-finite, and we isolate a small set of models whose nature remains unclear and requires further investigation. For these, we give some experimental results about their asymptotic behaviour, based on the inspection of a large number of initial terms. At least for some of them, the guessed asymptotic form seems to tip the balance towards non-D-finiteness.

Mathematics
CrossRef Open Access 2013
Coexistence of magnetic order and spin-glass-like phase in the pyrochlore antiferromagnet Na<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow/><mml:mn>3</mml:mn></mml:msub></mml:math>Co(CO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow/><mml:mn>3</mml:mn></mml:msub></mml:math>)<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow/><mml:mn>2</mml:mn></mml:msub></mml:math>Cl

Zhendong Fu, Yanzhen Zheng, Yinguo Xiao et al.

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