Hi Proud Sage Developers,
At the current Sage workshop some people (me, David Roe, Jen
Balakrishnan, etc.) have made a stopgap function and identified Trac
tickets describing "Bugs silently producing wrong answers". So far
they listed 7 of them: http://trac.sagemath.org/sage_trac/report/79
Do *you* know of such a bug in Sage that has not been classified as
such? Several of the ones listed below have been *known* for over 3
years.
* Trac 12718:
Somebody just pointed out this *doooozie* to me at ICERM [2] a few minutes ago
sage: R.<x,y> = QQ[]
sage: n=1000; f = x^n; f.subs(x = x^n)
x^1000000
sage: n=100000; f = x^n; f.subs(x = x^n)
x^1410065408*y^2
This looks like a serious libsingular bug.
* Trac 4942:
sage: f = x^2*log(x,2) - 1
sage: find_root(f, 0, 2)
0.0
sage: f.limit(x=0) # but 0 is not a root in any sense
-1
* Trac 9505:
sage: var('x,y,z'); f=x*y*z
(x, y, z)
sage: f.coeff(x)
y*z
sage: f.coeff(x*y)
0
This is by definition in GINAC (and Maxima), but is surprising and
confusing, e.g., one expects to get z above, and Mathematica does give
z.
* Trac 11358:
"matrix multiplication over ZZ sometimes gives incorrect results"
Yep.
I just posted a patch.
* Trac 11832:
sage: P3 = SteenrodAlgebra(p=3, profile=(lambda n: Infinity, lambda n: 1))
sage: P3._has_nontrivial_profile()
False
That's crazy? (I guess -- I have no clue whether it is crazy or not.)
There's a patch up.
* Trac 12509:
sage: K.<a> = NumberField(x^2-x-1); E = EllipticCurve([0, a + 1, 1,
28665*a - 46382, 2797026*a - 4525688])
sage: P = E([72*a - 509/5, -682/25*a - 434/25]); P.height()
1.35648516097058
sage: magma(E)(magma([P[0], P[1]])).Height()
1.38877711688727252538242306
The output from Sage is wrong after the 2 digit. Explicitly computing
to higher precision works fine, so some precision estimates in the
code are off.
* Trac 6667:
sage: K = Qp(2, prec=5)
sage: P.<x> = K[]
sage: f = P(x^4 + 2^3*x^3 + 2^13*x^2 + 2^21*x + 2^37)
sage: f.newton_polygon()
[(0, 37), (1, 21), (2, 13), (3, 3), (4, 0)]
This above is not even convex (the point (2,13) should not be there).
--
William Stein
Professor of Mathematics
University of Washington
http://wstein.org
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