fficient q-ary immuta

A fixed length code is called immutable if no codeword can be transformed into another codeword by using only a restricted set of symbol changes. Immutable codes are used to prevent undetectable updates of information stored over write-once memories 1141. In this paper we consider immutable codes on the alphabet Q = (0, . . . , q11. We prove that a maximum size immutable code of block length n can be obtained by taking the set of all vectors in Q” of weight rn(q 1)/21. Fu r th ermore, we propose an encoding rule to map information sequences of length k into codewords of an Immutable code of length k +p. The number k of information digits and the number p of parity digits must satisfy the inequality ks2(qPI)&1)-p. The proposed encoding algorithm has computational complexity O(k).