I am using SageMath version 9.2. I was trying the example in the documentation:
sage: k = GF(2)
sage: k.extension(x^1000 + x^5 + x^4 + x^3 + 1, 'a')
However, this gives the error: UnboundLocalError: local variable 'E' referenced before assignment
How do I fix this?
The extension method is really designed for towers of finite fields.
To define a finite field as an extension of the prime field,
one can use the GF or FiniteField constructor.
It can take an optional modulus argument:
sage: K.<a> = GF(2^1000, modulus=x^1000 + x^5 + x^4 + x^3 + 1)
For more information, read its documentation:
sage: GF?
or
sage: FiniteField?
Fixing the bug in the extension method reported in the question is tracked at:
Asked: 2021-03-18 15:59:04 +0100
Seen: 1,300 times
Last updated: Mar 24 '21
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Same behaviour with SageMath 9.3.beta9. This is a bug.
Is there any other way I can specify a finite field modulo a particular irreducible polynomial?
The code for the
extensionmethod of finite fields is atThere are a bunch of if/elif/else branches to decide how to define
E.In this case we are in the first branch of the main "if",
which has a nested if/elif/elif with no final "else", so that
Enever gets defined.