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Bug #918

UniversalGBasis: sometimes gives error

Added by John Abbott over 7 years ago. Updated over 7 years ago.

Status:
Closed
Priority:
Normal
Assignee:
Anna Maria Bigatti
Category:
Incomplete function
Target version:
CoCoA-5.2.0 spring 2017
Start date:
01 Sep 2016
Due date:
% Done:

100%

Estimated time:
2.05 h
Spent time:
1.95 h

Description

The following input produces an error (cannot index empty list)

S := support(sum(indets(R))^5);
J := RandomSubset(S,10);
I := ideal(J);
UniversalGBasis(I);

History

#1 Updated by John Abbott over 7 years ago

The code for UniversalGBasis simply makes the union of all the reduced GBases produced by GroebnerFanIdeals. Should there be a call to monic somewhere? Is it possible that the same poly appears but with different scalar factors? I know the reduced GBases are monic BUT only wrt. their own ordering.

#2 Updated by Anna Maria Bigatti over 7 years ago

try now (just checked it the new code using CallOnGroeberFan)

#3 Updated by John Abbott over 7 years ago

  • Status changed from New to In Progress
  • % Done changed from 0 to 10

A simpler failing case is:

S := support(sum(indets(R))^2);
J := RandomSubset(S,3);
I := ideal(J);
UniversalGBasis(I);

The problem is that MarkedPolynomialsToInequalitiesPostiveOrthant on line 69 of GroebnerFan.cpkg produces an empty list.

#4 Updated by Anna Maria Bigatti over 7 years ago

  • Status changed from In Progress to Feedback
  • Assignee set to Anna Maria Bigatti
  • % Done changed from 10 to 90

Fixed.
The list to create the matrix is empty (special case: monomial input), so CoCoA didn't know how to set the number of columns (yes, it makes sense to set the number of columns even if you have 0 rows).
So the function now call ZeroMat in that case.

#5 Updated by Anna Maria Bigatti over 7 years ago

  • Status changed from Feedback to Closed
  • % Done changed from 90 to 100

#6 Updated by Anna Maria Bigatti over 7 years ago

  • Estimated time set to 2.05 h

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