Then ψa ∈ HomFn and it has the following matrix

Abstract. In algebraic coding theory it is common practice to require that (n, q) = 1, where n is the word length and F = GF(q) is the alphabet. In this paper, which is about constacyclic codes, we shall stick to this practice too. Since linear codes have the structure of linear subspaces of Fn, an alternative description of constacyclic codes in terms of linear algebra appears to be another quite natural approach. Due to this description we derive lower bounds for the minimum distance of constacyclic codes that are generalizations of the well known BCH bound, the Hartmann-Tzeng bound and the Roos bound. Definition 1. Let a be a nonzero element of F = GF(q). A code C of length n over F is called constacyclic with respect to a, if whenever x = (c1, c2,..., cn) is in C, so is y = (acn, c1,..., cn−1). Let a be a nonzero element of F and let ψa