#9389: Bug in polynomials over residue fields (was: sage crashing when computing
local_data() for an EC)
-----------------------------+----------------------------------------------
Reporter: arminstraub | Owner: davidloeffler
Type: defect | Status: new
Priority: major | Milestone:
Component: number fields | Keywords: segfault polynomial finite field
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
-----------------------------+----------------------------------------------
Comment(by was):
In fact, after disabling the buggy ylchapuy code as follows, the original
elliptic curve example works.
1. The patch:
{{{
diff -r b5dab6864f35 sage/rings/polynomial/polynomial_ring.py
--- a/sage/rings/polynomial/polynomial_ring.py Sat Sep 04 21:40:16 2010
-0700
+++ b/sage/rings/polynomial/polynomial_ring.py Wed Oct 27 15:50:43 2010
-0700
@@ -1222,7 +1222,8 @@
"""
if implementation is None: implementation="NTL"
from sage.rings.finite_rings.finite_field_base import
is_FiniteField
- if implementation == "NTL" and is_FiniteField(base_ring):
+ # this is buggy as a florida swamp -- see trac 9389
+ if False and (implementation == "NTL" and
is_FiniteField(base_ring)):
p=base_ring.characteristic()
from sage.libs.ntl.ntl_ZZ_pEContext import ntl_ZZ_pEContext
from sage.libs.ntl.ntl_ZZ_pX import ntl_ZZ_pX
}}}
2. The result with this patch:
{{{
sage: K.<a> = QuadraticField(5)
sage: E = EllipticCurve(K,[1,2*a])
sage: E.local_data(K.ideal(2))
Local data at Fractional ideal (2):
Reduction type: bad additive
Local minimal model: Elliptic Curve defined by y^2 = x^3 + x + 2*a over
Number Field in a with defining polynomial x^2 - 5
Minimal discriminant valuation: 9
Conductor exponent: 5
Kodaira Symbol: I0*
Tamagawa Number: 1
sage: E.conductor()
Fractional ideal (544)
sage: E.tamagawa_numbers()
[1, 1]
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9389#comment:11>
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