Block intersection polynomials

Block intersection polynomials

We introduce the block intersection polynomial, which is constructed using certain information about a block design with respect to a subset S of its point-set, and then provides further information about the number of blocks intersecting S in exactly i points, for i = 0, . . . , |S|. We also discuss some applications of block intersection polynomials, including bounding the multiplicity of a b...

More on block intersection polynomials and new applications to graphs and block designs

The concept of intersection numbers of order r for t-designs is generalized to graphs and to block designs which are not necessarily t-designs. These intersection numbers satisfy certain integer linear equations involving binomial coefficients, and information on the nonnegative integer solutions to these equations can be obtained using the block intersection polynomials introduced by P.J. Came...

Intersection Alexander polynomials

By considering a (not necessarily locally-flat) PL knot as the singular locus of a PL stratified pseudomanifold, we can use intersection homology theory to define intersection Alexander polynomials, a generalization of the classical Alexander polynomial invariants for smooth or PL locally-flat knots. We show that the intersection Alexander polynomials satisfy certain duality and normalization c...

Block Intersection Numbers of Block Designs Ii

Edge-pancyclic block-intersection graphs

Alspach, B. and D. Hare, Edge-pancyclic block-intersection graphs, Discrete Mathematics 97 (1991) 17-24. It is shown that the block-intersection graph of both a balanced incomplete block design with block size at least 3 and A = 1, and a transversal design is edge-pancyclic.