On the equivalence of Z ^ps -linear generalized Hadamard codes

Linear codes of length n over Zps , p prime, called Zps -additive codes, can be seen as subgroups of Zn ps . A Zps -linear generalized Hadamard (GH) code is a GH code over Zp which is the image of a Zps -additive code under a generalized Gray map. It is known that the dimension of the kernel allows to classify these codes partially and to establish some lower and upper bounds on the number of such codes. Indeed, in this paper, for p ≥ 3 prime, we establish that some Zps -linear GH codes of length pt having the same dimension of the kernel are equivalent to each other, once t is fixed. This allows us to improve the known upper bounds. Moreover, up to t = 10 if p = 3 or t = 8 if p = 5, this new upper bound coincides with a known lower bound based on the rank and dimension of the kernel