Some results on quadratic residue codes over the ring.

Quadratic residue (QR) codes and their extensions over the finite non-chain ring are studied, where , is an odd prime and . A class of Gray maps preserving the self-duality of linear codes from to is given. Under a special Gray map, a self-dual code over , a formally self-dual code over and a formally self-dual code over are obtained from extended QR codes. [ABSTRACT FROM AUTHOR]