Some New Direct Constructions for \((\nu, \{5,\omega*\},1)\) PBDs

R. Julian R. Abel 1, Alan C.H. Ling 2
1School of Mathematics University of New South Wales Kensington, NSW 2033 Australia
2Combinatorics and Optimisation University of Waterloo Waterloo, Ontario Canada, N2L 3G1

Abstract

For \(\omega \leq 33\), the known necessary conditions for existence of a \((\nu,\{5,\omega^*\},1)\) PBD, namely \(\nu, \omega \equiv 1 \mod 4\), \(\nu \geq 4\omega+1\) and \(\nu \equiv \omega\) or \(4\omega +1 \mod 20\) are known to be sufficient in all but 26 cases. This paper provides several direct constructions which reduce the number of exceptions to 8.