Some two-weight codes invariant under the 3-fold covers of the Mathieu groups M22 and Aut(M22)
Abstract
Using an approach from finite group representation theory we construct quaternary non-projective codes with parameters [693,6,480]4,[1386,6,1008]4,[2016,6,1488]4, quaternary projective codes with parameters [231,6,160]4,[462,6,336]4 and [672,6,496]4 and binary projective codes with parameters [693,12,320]2,[1386,12,672]2,[2016,12,992]2 as examples of two-weight codes on which a finite almost quasisimple group of sporadic type acts transitively as permutation groups of automorphisms. In particular, we show that these codes are invariant under the 3-fold covers ˆ3M22 and ˆ3M22:2, respectively, of the Mathieu groups M22 and M22:2. Employing a known construction of strongly regular graphs from projective two-weight codes we obtain from the binary projective (respectively, quaternary projective) two-weight codes with parameters those given above, the strongly regular graphs with parameters (4096,693,152,110),(4096,1386,482,462), and (4096,2016,992,992), respectively. The latter graph can be viewed as a 2-(4096,2016,992)-symmetric design with the symmetric difference property whose residual and derived designs with respect to a block give rise to binary self-complementary codes meeting the Grey–Rankin bound with equality.
Communicated by A.-L. Horlemann
Dedicated to Joachim Rosenthal on the occasion of his 60th birthday