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[Axiom-developer] About finite fields


From: Fabio S.
Subject: [Axiom-developer] About finite fields
Date: Thu, 24 Oct 2013 11:38:05 +0200 (CEST)
User-agent: Alpine 2.02 (DEB 1266 2009-07-14)


I realized that when constructing finite fields providing a user choosen polynomial, Axiom doesn't check whether the used polynomial is irreducible or not.

For example:

(10) -> factor(x^8+x^4+x^2+x+1::PF 2)
(10) ->
           4    3       4    3    2
   (10)  (x  + x  + 1)(x  + x  + x  + x + 1)
                               Type: Factored(Polynomial(PrimeField(2)))
                                                             Time: 0 sec
(11) -> K:=FFP(PF 2,x^8+x^4+x^2+x+1)
(11) ->
   (11)  FiniteFieldExtensionByPolynomial(PrimeField(2),?^8+?^4+?^2+?+1)
                                                         Type: Domain
                                               Time: 0.01 (IN) = 0.01 sec
(12) -> size()$K
(12) ->
   (12)  256
                                                Type: NonNegativeInteger
                                                             Time: 0 sec
(13) -> a:=index(2)$K
(13) ->
   (13)  %A
   Type: FiniteFieldExtensionByPolynomial(PrimeField(2),?^8+?^4+?^2+?+1)
                                              Time: 0.01 (OT) = 0.01 sec
(14) -> minimalPolynomial a
(14) ->
          8    4    2
   (14)  ?  + ?  + ?  + ? + 1
                         Type: SparseUnivariatePolynomial(PrimeField(2))
                                                             Time: 0 sec
(15) -> (a^4+a^3+1)*(a^4+a^3+a^2+a+1)
(15) ->
   (15)  0
   Type: FiniteFieldExtensionByPolynomial(PrimeField(2),?^8+?^4+?^2+?+1)
                                                             Time: 0 sec


I am surprised that FiniteFieldByPolynomial allows a contruction which, clearly, has no sense and I am wondering if this has to be considered a bug to be fixed.

Fabio




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