Bug #1714
IsDivisible error (in QuotRing)
Description
Bernhard Andraschko reported by email the folllowing:
Use R ::= ZZ/(2)[x,y]; I := ideal(R, [i^2-i | i in indets(R)]); S := R/I; Use S; IsDivisible(x+y,x+y); // works OK IsDivisible(x+y,x+y+1); // index error!?!
The error is
--> ERROR: Row index out of range --> [CoCoALib] M(i,j) --> WHERE: at line 6 (column 6) of Anfdraschko-bug.cocoa5 --> /**/ IsDivisible(x+y,x+y+1); --> ^^^^^^^^^^^^^^^^^^^^^^
History
#1
Updated by John Abbott over 1 year ago
Updated by - Status changed from New to In Progress
- % Done changed from 0 to 10
Bug confirmed with current internal version.
Does not depend on char; same bug with other chars.
#2
Updated by John Abbott over 1 year ago
Simpler failing case:
p := 2; Use R ::= ZZ/(p)[x]; I := ideal(x^p-x); S := R/I; Use S; IsDivisible(x+1,x+1); // works OK IsDivisible(x,x+1); // index error!?!
#3
Updated by John Abbott over 1 year ago
The problem exists also in char 0
p := 3; Use R ::= QQ[x]; I := ideal(x^p-x); S := R/I; Use S; IsDivisible(x+1,x+1); // works OK IsDivisible(x,x+1); // index error!?!
#4
Updated by John Abbott over 1 year ago
I can also trigger NYI:
/**/ I := ideal(x^2); /**/ S := R/I; /**/ use S; /**/ IsDivisible(x, x+1); --> ERROR: NOT YET IMPLEMENTED -- please be patient, we're working on it --> [CoCoALib] SparsePolyRingBase::IdealImpl::myDivMod --> IsDivisible(x, x+1); --> ^^^^^^^^^^^^^^^^^^^
#5
Updated by John Abbott over 1 year ago
- Status changed from In Progress to Feedback
- Assignee set to John Abbott
- % Done changed from 10 to 90
Problem was in SparsePolyRingBase::IdealImpl::myDivMod (in file SparsePolyOps-idea.C)
We did not check for the case that there was no soln to the linear system.
BTW this function is very incomplete -- whence the NYI error above.
I'll check in shortly.
#6
Updated by John Abbott over 1 year ago
- Status changed from Feedback to Closed
- % Done changed from 90 to 100
- Estimated time set to 1.99 h
Added test (to exbugs.cocoa5).
Closing.