Finite fields defined by Conway polynomials: conversion of elements into subfields

[dkrenn]

We have

sage: from sage.rings.finite_rings.finite_field_givaro import FiniteField_givaro
sage: F9 = FiniteField_givaro(9)
sage: F81 = FiniteField_givaro(81)
sage: F81(F9.gen())
Traceback (most recent call last):
...
NotImplementedError

so one should implement this. Incidentally I did that, patch follows.

Apply

• attachment: trac_11938-5.11.beta1.patch

Depends on #13214

CC: @rbeezer @dimpase @jpflori @pjbruin @defeo

Component: finite rings

Keywords: finite field, givaro, Conway polynomial, conversion, coercion sd51

Author: Daniel Krenn

Reviewer: Jean-Pierre Flori

Issue created by migration from https://trac.sagemath.org/ticket/11938

[dkrenn]

comment:1

Attachment: trac_11938_conversion_gf_conway.patch.gz

Here comes the patch ;) Conversion is possible in both directions (up and down), see example below.

sage: from sage.rings.finite_rings.finite_field_givaro import FiniteField_givaro
sage: F4 = FiniteField_givaro(4,'b')
sage: F16 = FiniteField_givaro(16,'c')
sage: z = F4.gen() + F16.gen(); z
c^2
sage: z.parent()
Finite Field in c of size 2^4
sage: F4(z)
Traceback (most recent call last):
...
ValueError: c^2 is not a sub-field element            
sage: F4(z+F16.gen())
b

[dkrenn]

Author: Daniel Krenn

[loefflerd]

comment:3

I'm afraid this doesn't apply to the current Sage beta (see patchbot logs). I suspect it conflicts with #12084 (merged in 5.0.beta0).

[loefflerd]

Work Issues: needs rebase

[dkrenn]

Attachment: trac_11938_conversion_gf_conway.2.patch.gz

[dkrenn]

Description changed:

--- 
+++ 
@@ -10,3 +10,5 @@
 NotImplementedError
 ```
 so one should implement this. Incidentally I did that, patch follows.
+
+Apply trac_11938_conversion_gf_conway.2.patch