Symplectic Quasi Self-dual, Self-dual, and LCD Codes over Non-unital Rings of Order Six

Abstract

We consider codes over the two semi-local non-unital rings of order six, \[ H_{23} = \langle a,b \mid 2a=0, 3b = 0, a^2=a, b^2 = 0, ab = 0 = ba \rangle,\] and \[H_{32} = \langle a,b \mid 2a=0, 3b = 0, a^2=0, b^2 = b, ab = 0 = ba \rangle. \] with respect to a symplectic inner product. Via the decomposition $\mathcal{C} = a\,\mathcal{C}_a\oplus b\,\mathcal{C}_b$, any $H_z$-code splits into a binary component $\mathcal{C}_a$ and a ternary component $\mathcal{C}_b$; this yields characterizations of symplectic self-orthogonal, self-dual, and quasi self-dual (QSD) codes, and allows the introduction of symplectic nice and symplectic linear complementary dual (LCD) codes. Using the automorphism groups of $\mathcal{C}_a$ and $\mathcal{C}_b$ and double-coset enumeration, we classify, up to permutation equivalence, all symplectic self-orthogonal and QSD $H_z$-codes of short even lengths.