On codewords in the dual code of classical generalised quadrangles and classical polar spaces

Valentina Pepe, Leo Storme, Geertrui Van de Voorde
2010 Discrete Mathematics  
In [J.L. Kim, K. Mellinger, L. Storme, Small weight codewords in LDPC codes defined by (dual) classical generalised quadrangles, Des. Codes Cryptogr. 42 (1) (2007) 73 -92], the codewords of small weight in the dual code of the code of points and lines of Q(4, q) are characterised. Inspired by this result, using geometrical arguments, we characterise the codewords of small weight in the dual code of the code of points and generators of Q + (5, q) and H(5, q 2 ), and we present lower bounds on
more » ... weight of the codewords in the dual of the code of points and k-spaces of the classical polar spaces. Furthermore, we investigate the codewords with the largest weights in these codes, where for q even and k sufficiently small, we determine the maximum weight and characterise the codewords of maximum weight. Moreover, we show that there exists an interval such that for every even number w in this interval, there is a codeword in the dual code of Q + (5, q), q even, with weight w and we show that there is an empty interval in the weight distribution of the dual of the code of Q(4, q), q even. To prove this, we show that a blocking set of Q(4, q), q even, of size q 2 + 1 + r, where 0 < r < (q + 4)/6, contains an ovoid of Q(4, q), improving on [J. Eisfeld, L. Storme, T. Szőnyi, P. Sziklai, Covers and blocking sets of classical generalised quadrangles, Discrete Math. 238 (2001) 35-51, Theorem 9].
doi:10.1016/j.disc.2009.06.010 fatcat:bnyedbo35za2bffsgjjwenssjy