#7947: iteration error in QuadraticForm.vectors_by_length()
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Reporter: tornaria | Owner: tornaria
Type: defect | Status: new
Priority: major | Milestone: sage-4.3.1
Component: quadratic forms | Keywords:
Work_issues: | Author:
Upstream: N/A | Reviewer:
Merged: |
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After the fix in #7100 (rounding issues), there's still a bug in {{{the
vectors_by_length()}}} code:
{{{
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| Sage Version 4.3, Release Date: 2009-12-24 |
| Type notebook() for the GUI, and license() for information. |
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sage: Q = QuadraticForm(ZZ, 4, [1,-1,-1,-1, 1,0,0, 4,-3, 4])
sage: Q.vectors_by_length(3)
---------------------------------------------------------------------------
ValueError Traceback (most recent call
last)
/home/tornaria/.sage/temp/sage/9609/_home_tornaria__sage_init_sage_0.py in
<module>()
/home/tornaria/sage/sage-4.3/local/lib/python2.6/site-
packages/sage/quadratic_forms/quadratic_form__split_local_covering.pyc in
vectors_by_length(self, bound)
213 ## Now go back and compute the bounds...
214 ## 2. Compute bounds
--> 215 Z = (T[i] / Q[i][i]).sqrt(extend=False)
216 L[i] = ( Z - U[i]).floor()
217 x[i] = (-Z - U[i]).ceil()
/home/tornaria/sage/sage-4.3/local/lib/python2.6/site-
packages/sage/rings/real_double.so in
sage.rings.real_double.RealDoubleElement.sqrt
(sage/rings/real_double.c:10382)()
ValueError: negative number -0.888887555556 does not have a square root in
the real field
}}}
You can tell this is not a rounding issue from the error message.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7947>
Sage <http://www.sagemath.org>
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