#13714: multi_polynomial.lift(...) affects libsingular internal state; makes
ideal.complete_primary_decomposition() fail
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Reporter: Bouillaguet | Owner: malb
Type: defect | Status: new
Priority: major | Milestone: sage-5.5
Component: commutative algebra | Keywords: libsingular
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
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On sage 5.4:
{{{
sage: R.<x1,x2> = QQ[]
sage: I = R.ideal(x2**2 + x1 - 2, x1**2 - 1)
sage: R.one().lift(I)
[0, 0]
sage: I.complete_primary_decomposition()
// ** char_series returns 0 x 0 matrix from 3 input polys (0)
I[1,1]=x2^2+x1-2
I[1,2]=x1^2-1
}}}
and hangs forever (on sage 5.3 it just SEGFAULTs).
The key in this case is the '''failing''' call to {{{lift}}}, ''i.e.'',
evaluating {{{f.lift(I)}}} while `f` is not in `I`. What happens in these
case is changed by #13671 (but the problem in this ticket is independent).
It was found while fixing #13671 that when computing {{{f.lift(I)}}}, then
if `f` is not in `I` an error is raised by singular, by setting a global
variable. Before #13671, this variable was not reset, and subsequent calls
to lift would return junk. After #13671, the global variable is reset and
``lift`` works correctly. However, it was apparently not the end of the
story.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13714>
Sage <http://www.sagemath.org>
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