Opened 9 years ago
Last modified 2 weeks ago
#12529 positive_review defect
libsingular reduces polynomials incompletely
Reported by:  SimonKing  Owned by:  malb 

Priority:  major  Milestone:  sage9.2 
Component:  commutative algebra  Keywords:  multivariate polynomial reduction 
Cc:  malb  Merged in:  
Authors:  Samuel Lelièvre  Reviewers:  Kiran Kedlaya 
Report Upstream:  N/A  Work issues:  
Branch:  public/12529 (Commits)  Commit:  5b3253a14e46a97e783d5800cc20898bd1bb6957 
Dependencies:  Stopgaps:  todo 
Description (last modified by )
Condensed version of a report by Oleksandr Kazymyrov on sagesupport.
Define g
by modding out in a multivariate polynomial ring:
sage: gens = 'y a0 a1 a2 b0 b1 b2 c1 c2 d0 d1 d2 d3 d4 d5 d6 d7'.split() sage: R = PolynomialRing(GF(8), 17, gens) sage: R.inject_variables(verbose=False) sage: A, B, C = a0 + a1*y + a2*y^2, b0 + b1*y + b2*y^2, c1*y + c2*y^2 sage: D = d0 + d1*y + d2*y^2 + d3*y^3 + d4*y^4 + d5*y^5 + d6*y^6 + d7*y^7 sage: F = D.subs({y: B}) sage: G = A.subs({y: F}) + C sage: g = G.mod(y^8 + y)
After modding out by a polynomial of degree 8 in y
,
the degree of g
in y
should be at most 7.
Up to Sage 9.1.rc1:
sage: g.degree(y) 14
After #27508 (Force tail reduction in polynomial quotient ring), merged in Sage 9.1.rc2:
sage: g.degree(y) 7
The problem was libsingular not doing tail reduction when calling Singular.
This ticket adds the above example as a doctest.
Change History (12)
comment:1 Changed 9 years ago by
 Priority changed from blocker to critical
comment:2 Changed 7 years ago by
 Milestone changed from sage5.11 to sage5.12
comment:3 Changed 7 years ago by
 Milestone changed from sage6.1 to sage6.2
comment:4 Changed 6 years ago by
 Milestone changed from sage6.2 to sage6.3
comment:5 Changed 6 years ago by
 Milestone changed from sage6.3 to sage6.4
comment:6 Changed 5 years ago by
 Stopgaps set to todo
comment:7 Changed 6 weeks ago by
I just tried this and got an answer consistent with Singular. Maybe close this as a duplicate?
comment:8 Changed 2 weeks ago by
 Milestone changed from sage6.4 to sage9.3
 Priority changed from critical to major
Condensed version of the initial report, as a tentative doctest:
sage: gens = 'y a0 a1 a2 b0 b1 b2 c1 c2 d0 d1 d2 d3 d4 d5 d6 d7'.split() sage: R = PolynomialRing(GF(8), 17, gens) sage: R.inject_variables(verbose=False) sage: A, B, C = a0 + a1*y + a2*y^2, b0 + b1*y + b2*y^2, c1*y + c2*y^2 sage: D = d0 + d1*y + d2*y^2 + d3*y^3 + d4*y^4 + d5*y^5 + d6*y^6 + d7*y^7 sage: F = D.subs({y: B}) sage: G = A.subs({y: F}) + C sage: g = G.mod(y^8 + y) sage: g.degree(y) 7
This was fixed by #27508 (Force tail reduction in polynomial quotient ring).
It was merged in Sage 9.1.rc2, from which version on we get the correct value: 7.
In Sage <= 9.1.rc1, we get an incorrect value: 14.
If someone can suggest where to locate this doctest, I can push a branch.
Priority down from critical to major: bug fixed, only a doctest is needed.
comment:9 Changed 2 weeks ago by
I would suggest to put the doctest in sage/rings/polynomial/polynomial_element.pyx
under mod
or __mod__
.
comment:10 Changed 2 weeks ago by
 Branch set to public/12529
 Commit set to 5b3253a14e46a97e783d5800cc20898bd1bb6957
 Description modified (diff)
 Milestone changed from sage9.3 to sage9.2
 Status changed from new to needs_review
Please review and add reviewer name.
Let's see if this can get in Sage 9.2.
New commits:
5b3253a  Add doctest for remainder in multivariate polynomial ring

comment:11 Changed 2 weeks ago by
 Reviewers set to Kiran Kedlaya
 Status changed from needs_review to positive_review
No complaints from patchbot, nor from me.
I don't believe all basic arithmetic failures should be blockers, and it's dubious that this issue is even about "basic" arithmetic.