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Bug #279

Bug in Radical (actually a RingHom problem)

Added by Anna Maria Bigatti over 11 years ago. Updated over 9 years ago.

Status:
Closed
Priority:
Normal
Category:
Incomplete function
Target version:
Start date:
29 Nov 2012
Due date:
% Done:

100%

Estimated time:
20.00 h
Spent time:

Description

this gives an error:

/**/ M:=6;  Use R::=QQ[x[1..M,1..M]], DegLex;
/**/ J := ***Ideal(
x[2,4]x[3,6] - x[2,6]x[3,4],
x[1,3]x[2,4] - x[1,4]x[2,3],
x[1,2]x[4,3] - x[1,3]x[4,2],
x[1,2]x[5,4] - x[1,4]x[5,2],
x[2,4]x[5,5] - x[2,5]x[5,4],
x[1,1]x[3,4] - x[1,4]x[3,1],
x[2,3]x[6,5] - x[2,5]x[6,3]
)***;

/**/  Poincare(R/J); 
/**/  RJ := Radical(J); 


Related issues

Related to CoCoALib - Bug #190: Subtle ref count bug for poly rings (via CoeffEmbeddingHom)Closed2012-06-19

Related to CoCoA-5 - Bug #382: Subtle bug with CoeffEmbeddingHomClosed2013-06-27

History

#1 Updated by Anna Maria Bigatti over 11 years ago

  • Category set to Incomplete function

#2 Updated by John Abbott over 10 years ago

Here are two more problem cases with radical

Use ZZ/(2)[x,y,z];
I := ideal(x+y,x-y);
radical(I);

Prints out some junk!
J := ideal(x^2 +y^2, x^2 +z^2, y^2 +z^2);
radical(J);

Complains about an empty list of gens for an ideal.

Now that SqfreeFactor has been implemented; it should be possible to fix radical.
20140903 fixed

#3 Updated by John Abbott about 10 years ago

Here's an old(?) failing case; posting here so that we have a test suite.

Use R::=ZZ/(2)[a,b,c,d,e,f,g,h,i,j,k,l,m,n,o];

A:=Mat([
[0,a,b,c,d],
[a,0,f,g,h],
[b,f,0,j,k],
[c,g,j,0,m],
[d,h,k,m,0]
]);

B:=Mat([
[0,f,g,h,i],
[f,0,j,k,l],
[g,j,0,m,n],
[h,k,m,0,o],
[i,l,n,o,0]
]);

J:=Ideal(Minors(A,4))+Ideal(Minors(B,4));
JJ:=Radical(J); JJ;

20140121: in C5 gives error Empty List in ctor for ideal
20140903: fixed

#4 Updated by Anna Maria Bigatti almost 10 years ago

  • Target version set to CoCoA-5.1.0 Easter14

#5 Updated by John Abbott almost 10 years ago

  • Target version changed from CoCoA-5.1.0 Easter14 to CoCoA-5.1.1 Seoul14

#6 Updated by John Abbott almost 10 years ago

  • Status changed from New to In Progress
  • % Done changed from 0 to 10
  • Estimated time set to 20.00 h

20140514 JAA confirms that the original problem persists; also gives numerous memory alloc errors like this:

CoCoAInterpreter(5397) malloc: *** error for object 0x101af8ba0: incorrect checksum for freed object - object was probably modified after being freed.

#7 Updated by John Abbott almost 10 years ago

Here is an excerpt from CoCoA (this morning, 20140624)

>>> I:=ideal(x*y-1,(x-2)^2+(y-2)^2-2);

>>> ReducedGBasis(I);
[x*y -1, x^2 +y^2 -4*x -4*y +6, y^3 -4*y^2 +x +6*y -4]

>>> radical(I);
ideal(x*y -1, x^2 +y^2 -4*x -4*y +6, x -1)

>>> radical(I+ideal(z));
ideal(z, y -1, x -1)

20140625 Renzo pointed out that the result is correct but "poorly presented"; the result is indeed ideal(x-1,y-1)
20140903 this is a problem due to the output of GBasis (therefore intersect) for non-homogenous input

#8 Updated by Anna Maria Bigatti over 9 years ago

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

found the bug: usual ref-count bug on RINGHOM.
Found a few more little bugs in the way ;-)

#9 Updated by Anna Maria Bigatti over 9 years ago

  • Subject changed from Radical to Bug in Radical (actually a RingHom problem)
  • Status changed from Feedback to Closed
  • % Done changed from 90 to 100

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