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math.CO updates on arXiv.org

Complement Submodular Information Measures for Balanced and Robust Data Selection A Proof of a Conjecture on Positive and Negative Square Energies of Unicyclic Graphs Laplacian Spectrum of the Weakly Zero-Divisor Graph of a Finite Commutative Ring An identity for second Eulerian numbers via lattice-point counting $t$-tone edge coloring of graphs Constructing Maximal Bumpless Pipedreams for Double Grothendieck Polynomials Mubayi's Polynomial-Ideal Conjecture and Cover-Ideal Turán Methods Implicit Binarization via Complex Phase Dynamics in Combinatorial Optimization The limits of Schur multipliers in Pólya conversion problems for the $q$-permanent function Universality theorems for generalized splines Framing Triangulations for Arbitrary Integer Flow Polytopes On the Common Generalization of Gentle Algebras and Framed Directed Acyclic Graphs The complexity of frugal digraph homomorphisms Chaotic and periodic behavior of jeu de taquin on infinite Young tableaux Enumerating Pattern Avoiding Parking Functions Incidence toric ideals and three-point functions Unique Winning Opening Move in Three-Row Chomp Strong majority colorings of graphs A Balancing Theorem for Spanning Trees of Rectangular Grid Graphs Spectral radius and edge-disjoint connected factors of graphs New invariants for rank metric codes, with applications to the classification of rank two semifields of order 256 Flexible DP-4-coloring of planar graphs without 4-cycles and intersecting triangles Balanced intersection size distributions in projective planes List Reconstruction Problem with List Size Two Is Dimensionality a Barrier for Retrieval Models? The INIEP: Irreducible and Positive Realizations The number of Pfaffian orientations on punctured polygonally cellulated surfaces Explicit Construction of Polytopes whose Ehrhart Polynomials Realize any Given Sign Pattern Finite-state enumeration of adjacency-constrained 132-avoiding permutations AMDS and quantum AMDS Constacyclic codes of length $4p^ς$ over $\mathbb{F}_{{p}^{m}}$
Design Theory and Some Non-simple Forbidden Configurations
R. P. Anstee, Farzin Barekat · 2019-09-17 · via math.CO updates on arXiv.org

Let 1_k 0_l denote the (k+l)\times 1 column of k 1's above l 0's. Let q. (1_k 0_l) $ denote the (k+l)xq matrix with q copies of the column 1_k0_l. A 2-design S_λ(2,3,v) can be defined as a vx(λ/3)\binom{v}{2} (0,1)-matrix with all column sums equal 3 and with no submatrix (λ+1).(1_20_0). Consider an mxn matrix A with all column sums in {3,4,... ,m-1}. Assume m is sufficiently large (with respect to λ) and assume that A has no submatrix which is a row permutation of (λ+1). (1_2 0_1). Then we show the number of columns in A is at most (λ)/3)\binom{m}{3} with equality for A being the columns of column sum 3 corresponding to the triples of a 2-design S_λ(2,3,m). A similar results holds for(λ+1). (1_2 0_2). Define a matrix to be simple if it is a (0,1)-matrix with no repeated columns. Given two matrices A, F, we define A to have F as a configuration if and only if some submatrix of A is a row and column permutation of F. Given m, let forb(m,q.(1_k 0_l)) denote the maximum number of possible columns in a simple m-rowed matrix which has no configuration q.(1_k 0_l). For m sufficiently large with respect to q, we compute exact values for forb(m,q.(1_1 0_1)), forb(m,q.(1_2 0_1)), forb(m,q.(1_2 0_2)). In the latter two cases, we use a construction of Dehon (1983) of simple triple systems S_λ(2,3,v) for λ>1. Moreover for l=1,2, simple mxforb(m,q.(1_2 0_l)) matrices with no configuration q.(1_2 0_l) must arise from simple 2-designs S_λ(2,3,m) of appropriate λ. The proofs derive a basic upper bound by a pigeonhole argument and then use careful counting and Turan's bound, for large m, to reduce the bound. For small m, the larger pigeonhole bounds are sometimes the exact bound. There are intermediate values of m for which we do not know the exact bound.