Sage's new generic HNF doesn't quite work right wrt the free modules code

[williamstein]

The last output below should obviously be True, but it is False.

sage: R.<x> = GF(7)[]
sage: A = R^3
sage: L = A.span([x*A.0 + (x^3 + 1)*A.1, x*A.2]); L
Free module of degree 3 and rank 2 over Univariate Polynomial Ring in x over Finite Field of size 7
Echelon basis matrix:
[      x x^3 + 1       0]
[      0       0       x]
sage: M = A.span([x*L.0]); M
Free module of degree 3 and rank 1 over Univariate Polynomial Ring in x over Finite Field of size 7
Echelon basis matrix:
[    x^2 x^4 + x       0]
sage: M.0 in L
False

Apply trac_9053_fixes_pivots.v2.patch

CC: @mminzlaff

Component: linear algebra

Author: Moritz Minzlaff

Reviewer: Keshav Kini

Merged: sage-4.7.alpha4

Issue created by migration from https://trac.sagemath.org/ticket/9053

[mminzlaff]

comment:2

Attachment: trac_9053_fixes_pivots.patch.gz

The bug was a single line in _echelon_form_PID which returned the wrong pivot element for matrices of one row. The attached patch should fix that.

While doctesting all of Sage I received two errors (that seem unrelated?):

The following tests failed:

        sage -t  -long -force_lib devel/sage/sage/schemes/elliptic_curves/gal_reps.py # Time out
        sage -t  -long -force_lib devel/sage/sage/interfaces/sage0.py # 2 doctests failed

The first apparently also came up during discussions on #9390. The doctest failure in sage0.py "randomly" appeared or not when I reran the test mutiple times. I'm not quite sure what to make of this...

[mminzlaff]

Author: Moritz Minzlaff

[mminzlaff]

comment:3

I just reran the above two doctests on a different machine and receieved no doctest failures. shrug

[kini]

line wrapping

[kini]

comment:4

Attachment: trac_9053_fixes_pivots.v2.patch.gz

I can't replicate your doctest failures. Everything passes on sage.math, except the ever-troublesome devel/sage/sage/tests/startup.py , which I tried again individually with no problems. The fix itself looks good. Reference builds, though how that could be affected I don't know. IIRC all code should be within 79 columns, so I split some lines in this function for you while you're at it. Feel free to rewrite it if it looks ugly, haha.

[kini]

Reviewer: Keshav Kini

[kini]

comment:5

(for patchbot...)

[jdemeyer]

Merged: sage-4.7.alpha4