题目： q-ary cyclic constant-weight codes
A cyclic (n,d,w)_q code is a q-ary cyclic code of length n, minimum Hamming distance d and
weight w. Let CA_q(n,d,w) denote the largest possible number of codewords in a cyclic
(n,d,w)_q code. A cyclic (n,d,w)_q code is said to be optimal if it contains
CA_q(n,d,w) codewords. In this talk we give several constructions of optimal cyclic
(n,d,w)_q code by difference methods. We also mention that the exact value of
CA_q(n,d,w) are determined for some specific parameters.