Bug #1248
MinPolyQuot: guaranteed and ideal without GBasis
Description
Today we noticed that ex-Verification1
failed. What happened is that MinPolyQuot
was called with a (principal) ideal without a G-basis. Comparison was made between the result obtained with VerificationLevel
set to 0, set to 2 and set to "guaranteed".
The answer was wrong with "guaranteed".
Fix this!
Related issues
History
#1 Updated by John Abbott over 5 years ago
- (A) if the ideal supplied has no G-basis then verification was disabled (since verification would entail computing a G-basis, which might be very costly)
- (B) if the
VerificationLevel
is set toguaranteed
then the result should always be correct.
Anna asks what should happen of the caller does not specify what VerificationLevel
to use? Previously the heuristic (A) was used.
#2 Updated by John Abbott over 5 years ago
- Related to Support #1240: John's visit Feb 2019 added
#3 Updated by John Abbott over 5 years ago
- Related to Feature #1103: Pseudo-zero-dim ideals added
#4 Updated by John Abbott over 5 years ago
For min polys it might be possible to work with a sub-ideal in a subring. For example,
use QQ[x,y,z,t]; I := ideal(x^2-2, y^3-3, z^5-5); f := x+y; MinPolyQuot(f,I,x);
------ this comment has been converted into Feature #1254 ------
#5 Updated by John Abbott over 5 years ago
- Status changed from New to In Progress
- % Done changed from 0 to 10
- (1) my preference is that computations in CoCoALib be guaranteed correct unless the caller explicitly says otherwise (e.g. by specifying a finite
VerificationLevel
). - (2) I forgot to mention that in the case that a guaranteed answer is desired and the ideal has no GBasis,
MinPolyQuot
could perhaps map the ideal into another ring withDegRevLex
, and compute the min poly there (because computing a GBasis in the original ring might be costly if the term-ordering is inconvenient)
#6 Updated by John Abbott over 5 years ago
The CoCoA-5 test test-ApproxSolve.cocoa5
failed with wrong output: there should have been no output, instead a warning about "no precomputed GBasis" is printed 88 times!
This should be fixed.
#7 Updated by Anna Maria Bigatti over 5 years ago
Fixed.
Now, guaranteed computes GBasis if missing, so result is guaranteed.
Testing.
#8 Updated by Anna Maria Bigatti over 5 years ago
- % Done changed from 10 to 70
#9 Updated by Anna Maria Bigatti over 5 years ago
- Related to deleted (Feature #1103: Pseudo-zero-dim ideals)
#10 Updated by John Abbott almost 5 years ago
- Assignee set to Anna Maria Bigatti
We should either close this issue (almost immediately), or postpone it (to 0.99700?).
#11 Updated by John Abbott almost 5 years ago
- Related to Design #849: Cleanup MinPoly code added
#12 Updated by Anna Maria Bigatti over 4 years ago
- Status changed from In Progress to Feedback
- % Done changed from 70 to 90
#13 Updated by Anna Maria Bigatti over 4 years ago
- Status changed from Feedback to Closed
- % Done changed from 90 to 100