id,summary,reporter,owner,description,type,status,priority,milestone,component,resolution,keywords,cc,merged,author,reviewer,upstream,work_issues,branch,commit,dependencies,stopgaps
13714,multi_polynomial.lift(...) affects libsingular internal state; makes ideal.complete_primary_decomposition() fail,Bouillaguet,malb,"On sage 5.5:
{{{
sage: R. = QQ[]
sage: I = R.ideal(x2**2 + x1 - 2, x1**2 - 1)
sage: R.one().lift(I)
Traceback (most recent call last):
...
ValueError: polynomial is not in the ideal
}}}
And then the bug:
{{{
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 SEGFAULTed).
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 this case has been 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.",defect,closed,major,sage-5.7,commutative algebra,fixed,libsingular,malb mstreng,sage-5.7.beta4,Charles Bouillaguet,"Martin Albrecht, Marco Streng",N/A,,,,,