#8505: random points on elliptic curve misses half the group
-------------------------------+--------------------------------------------
Reporter: robertwb | Owner: cremona
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.3.4
Component: elliptic curves | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
-------------------------------+--------------------------------------------
Comment(by cremona):
I tested all sage/schemes/elliptic_curves with -long and had one failure:
{{{
j...@selmer%sage -t -long
"sage/schemes/elliptic_curves/ell_finite_field.py"
**********************************************************************
File "/storage/jec/sage-4.3.4.alpha1/devel/sage-
tests/sage/schemes/elliptic_curves/ell_finite_field.py", line 1269:
sage: E.gens()
Expected:
((0 : 7 : 1),)
Got:
((0 : 4 : 1),)
**********************************************************************
File "/storage/jec/sage-4.3.4.alpha1/devel/sage-
tests/sage/schemes/elliptic_curves/ell_finite_field.py", line 1423:
sage: for p in prime_range(10000): #long time (~20s)
if p != Integer(389):
G=E.change_ring(GF(p)).abelian_group()
Exception raised:
Traceback (most recent call last):
File "/home/jec/sage-current/local/bin/ncadoctest.py", line 1231, in
run_one_test
self.run_one_example(test, example, filename, compileflags)
File "/home/jec/sage-current/local/bin/sagedoctest.py", line 38, in
run_one_example
OrigDocTestRunner.run_one_example(self, test, example, filename,
compileflags)
File "/home/jec/sage-current/local/bin/ncadoctest.py", line 1172, in
run_one_example
compileflags, 1) in test.globs
File "<doctest __main__.example_24[17]>", line 3, in <module>
G=E.change_ring(GF(p)).abelian_group()
File "/home/jec/sage-current/local/lib/python/site-
packages/sage/schemes/elliptic_curves/ell_finite_field.py", line 1512, in
abelian_group
Q = self.random_point()
File "/home/jec/sage-current/local/lib/python/site-
packages/sage/schemes/elliptic_curves/ell_finite_field.py", line 380, in
random_element
v = self.lift_x(k.random_element(), all=True)
File "/home/jec/sage-current/local/lib/python/site-
packages/sage/schemes/elliptic_curves/ell_generic.py", line 836, in lift_x
return [self.point([x, (-b+d)/2, one], check=False) for d in
D.sqrt(all=True)]
TypeError: 'sage.rings.integer_mod.IntegerMod_int' object is not
iterable
**********************************************************************
File "/storage/jec/sage-4.3.4.alpha1/devel/sage-
tests/sage/schemes/elliptic_curves/ell_finite_field.py", line 336:
sage: P = E.random_element(); P
Expected:
(751 : 10581 : 1)
Got:
(16740 : 12486 : 1)
**********************************************************************
File "/storage/jec/sage-4.3.4.alpha1/devel/sage-
tests/sage/schemes/elliptic_curves/ell_finite_field.py", line 347:
sage: P = E.random_element(); P
Expected:
(a^3 + a + 5 : 5*a^4 + 6*a^3 + 5*a^2 + 3*a + 6 : 1)
Got:
(2*a^4 + 3*a^3 + 5*a^2 + 6*a + 4 : 6*a^4 + 4*a^3 + a + 6 : 1)
**********************************************************************
File "/storage/jec/sage-4.3.4.alpha1/devel/sage-
tests/sage/schemes/elliptic_curves/ell_finite_field.py", line 358:
sage: P = E.random_element(); P
Expected:
(a^4 + a^3 + a : 1 : 1)
Got:
(a^4 + a^2 + 1 : a^3 + a : 1)
**********************************************************************
3 items had failures:
1 of 10 in __main__.example_21
1 of 25 in __main__.example_24
3 of 20 in __main__.example_9
***Test Failed*** 5 failures.
For whitespace errors, see the file
/home/jec/.sage//tmp/.doctest_ell_finit
}}}
These are all but one trivial and I'll fix them with a reviewer patch.
But the other one looks stranger. So some more investigation is
required...watch this space!
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8505#comment:3>
Sage <http://www.sagemath.org>
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