On the Category of Group Codes
  For the category of group codes, that generalizes the category of linear codes over a finite field, and with the generalized notions of direct sums and ndecomposable group codes, we prove that every MDS non trivial code, every perfect non trivial code, and every constant weight nondegenerate group code are indecomposable. We prove that every group code is a direct sum of indecomposable group codes, and using this result we obtain the automorphism groups of any group code in terms of its decomposition in indecomposable components. We conclude with the determination of the structure of decomposable cyclic group codes. 
Rolando G\'omez Macedo and Felipe Zald\'ivar
cs.IT math.IT