Abstract
A Ryser design on v points is a collection of proper subsets (called blocks) of a point-set with points satisfying (i) every two blocks intersect each other in points for a fixed (ii) there are at least two block sizes. A design is called a symmetric design, if all the blocks of have the same size (or equivalently, every point has the same replication number) and every two blocks intersect each other in points. The only known construction of a Ryser design is via block complementation of a symmetric design. Such a Ryser design is called a Ryser design of Type-1. The main results of the present article are the following. An expression for the inverse of the incidence matrix of a Ryser design is obtained. A necessary condition for the design to be of Type-1 is obtained. A well known conjecture states that, for a Ryser design on points . Partial support for this conjecture is obtained. Finally, a special case of Ryser designs with two block sizes is shown to be of Type-1.
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Disclosure statement
No potential conflict of interest was reported by the authors.