Pierre Loidreau
INRIA, projet CODES
BP 105
78153 Le Chesnay Cedex, France Pierre.Loidreau@inria.fr
Journée ATI,
Marseille, France, 1999
Abstract
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.