On weighing matrices with square weights

We give a new construction for a known family of weighing matrices using the 2-adjugate method of Vartak and Patwardhan. We review the existence of W(n,k²), k = 1,.. ,12, giving new results for k = 8,...12

Spectrum of Sizes for Perfect Deletion-Correcting Codes

One peculiarity with deletion-correcting codes is that perfect $t$-deletion-correcting codes of the same length over the same alphabet can have different numbers of codewords, because the balls of radius $t$ with respect to the Levenshte\u{\i}n distance may be of different sizes. There is interest, therefore, in determining all possible sizes of a perfect $t$-deletion-correcting code, given the length $n$ and the alphabet size~$q$. In this paper, we determine completely the spectrum of possible sizes for perfect $q$-ary 1-deletion-correcting codes of length three for all $q$, and perfect $q$-ary 2-deletion-correcting codes of length four for almost all $q$, leaving only a small finite number of cases in doubt.Comment: 23 page

A note on orthogonal designs

We extend a method of Kharaghani and obtain some new constructions for weighing matrices and orthogonal designs. In particular we show that if there exists an OD(s1,...,sr), where w = ∑si, of order n, then there exists an OD(s1w,s2w,...,8rw) of order n(n+k) for k ≥ 0 an integer. If there is an OD(t,t,t,t) in order n, then there exists an OD(12t,12t,12t,12t) in order 12n. If there exists an OD(s,s,s,s) in order 4s and an OD(t,t,t,t) in order 4t there exists an OD(12s²t,12s²t,12s²t,12s²t) in order 48s²t and an OD(20s²t,20s²t,20s²t20s²) in order 80s²t

The Journey of the Union-Closed Sets Conjecture

We survey the state of the union-closed sets conjecture