Codes dérivés de certains codes de Goppa

Pierre Loidreau

BP 105
78153 Le Chesnay Cedex, France

Journée ATI,
Marseille, France, 1999


When the generating polynomial of a Goppa code has coefficient in a subfield of the support field, the automorphism group of the code is not trivial. Namely it contains the group generated by the Frobenius automorphism. Moreover the set of the words that are invariant by the action of the Frobenius is a non-trivial subcode. By projecting every orbit of the support, one obtains a code of smaller parameters denoted s-projected code.