The Isometry-Dual Property in Flags of Two-Point Algebraic Geometry Codes

Identifier:  imarina:9231697

Handle: https://hdl.handle.net/20.500.11797/imarina9231697

Authors:  Bras-Amoros, M; Castellanos, AS; Quoos, L

Abstract:
A flag of codes C0 ⊊ C1 ⊊ ... ⊊ Cs ⊆ Fnq is said to satisfy the isometry-dual property if there exists x ∈ (F*q)n such that the code Ci is x-isometric to the dual code C⊥s-i for all i = 0, ..., s. For P and Q rational places in a function field F, we investigate the existence of isometry-dual flags of codes in the families of two-point algebraic geometry codes CL(D, a0P + bQ) ⊊ CL(D, a1P + bQ) ⊊ ...⊊ CL(D, asP + bQ), where the divisor D is the sum of pairwise different rational places of F and P,Q are not in supp(D). We characterize those sequences in terms of b for general function fields. We then apply the result to the broad class of Kummer extensions F defined by affine equations of the form ym = f(x), for f(x) a separable polynomial of degree r, where gcd(r,m) = 1. For P the rational place at infinity and Q the rational place associated to one of the roots of f(x), and for D an Aut(F/Fq)-invariant sum of rational places of F, such that P,Q ∉ suppD, it is shown that the flag of two-point algebraic geometry codes has the isometry-dual property if and only if m divides 2b + 1. At the end we illustrate our results by applying them to two-point codes over several well know function fields.