An algorithm for the k-error linear complexity of a sequence with period   2pn over GF(q)
  The union cost is used, so that an efficient algorithm for computing the k-error linear complexity of a sequence with period 2pn over GF(q) is presented, where p and q are odd primes, and q is a primitive root of modulo p2. 
Jianqin Zhou, Xirong Xu