On the automorphism groups of affine-invariant codes

Using the classification of finite simple groups, the author obtains a condition for a permutation group on a finite field GF(p^m ) which is necessary to have the affine group AGL(1,p^m) as a subgroup. Applying this result to the automorphism groups of non trivial affine-invariant codes, the author proves that the automorphism groups discussed are always subgroups of the general affine group AGL(m,p)