Self-orthogonal codes over Z4 arising from the chain ring Z4[u]/〈u2+1〉

Abstract We find a building-up type construction method for self-orthogonal codes over Z 4 arising from the chain ring Z 4 [ u ] / 〈 u 2 + 1 〉 . Our construction produces self-orthogonal codes over Z 4 with increased lengths and free ranks from given self-orthogonal codes over Z 4 with smaller lengths and free ranks; in the most of the cases their minimum weights are also increased. Furthermore, any self-orthogonal code over Z 4 with generator matrix subject to certain conditions can be obtained from our construction. Employing our construction method, we obtain at least 125 new self-orthogonal codes over Z 4 up to equivalence; among them, there are 35 self-orthogonal codes which are distance-optimal. Furthermore, we have eight self-orthogonal codes, which are distance-optimal among all linear codes over Z 4 with the same type. As a method, we use additive codes over the finite ring Z 4 [ u ] / 〈 u 2 + 1 〉 with generator matrices G satisfying G G T = O , and we use a new Gray map from Z 4 [ u ] / 〈 u 2 + 1 〉 to Z 4 3 as well.