Project

General

Profile

Bug #1281

Factor of multivariate sometimes prints ERROR

Added by John Abbott almost 5 years ago. Updated 3 months ago.

Status:
New
Priority:
High
Assignee:
-
Category:
Maths Bugs
Target version:
CoCoALib-0.99880
Start date:
04 May 2019
Due date:
% Done:

10%

Estimated time:
Spent time:
1.20 h

Description

Here is an example:

use QQ[x,y];
f := -x^4*y^3 -x^2*y +1;
facs := factor(f); --> do this 97 times
ERROR: maximum deg in destination polynomial too low

Despite the error message, the answer seems to be correct.

History

#1 Updated by John Abbott almost 5 years ago

The simplest examples (with 3 terms) seem to be of deg 7 (none found in deg 6 or deg 5).

-x^6*y -x^2 +1
-x^6*y -x^5*y +1
-x^4*y^3 -x^2*y +1
-x^5*y^2 +x^3*y +1

The signs of the coeffs seem to be important: I found no example with all coeffs equal to +1.

Just found a lower deg example:

-x^4*y +x^2 +x +1
x^4*y +x^3*y -x^2 +2
-x^4*y +x^4 -x^2 +x +1
-x^4*y -x^3*y -x^2*y -x^2 +1

There seem to be only 2 examples in deg 5 with 4 terms.

The error mesg can be produced by fns in one of two files:
  • DUPZexgcd.c
  • DUPZinterp.c
    The relevant line is a call to JERROR with arg JERROR_DEG_TOO_LOW

#2 Updated by John Abbott over 4 years ago

  • Target version changed from CoCoALib-0.99700 to CoCoALib-0.99800

#3 Updated by John Abbott over 3 years ago

  • Target version changed from CoCoALib-0.99800 to CoCoALib-0.99850

#4 Updated by Anna Maria Bigatti over 2 years ago

I confirm I (rarely) meet this error with tough examples in our development of Comprehensive Groebner Systems.

#5 Updated by Anna Maria Bigatti over 2 years ago

When it happens, it happens in pairs. Run this:

for i := 1 to 1000 do
  facs := factor(x^6*y +x^2 -1);
  println i,  facs.RemainingFactor = 1, facs.factors = [x^6*y +x^2 -1],
          facs.multiplicities = [1];
endfor;

#6 Updated by Anna Maria Bigatti over 2 years ago

  • % Done changed from 0 to 10

#7 Updated by John Abbott 3 months ago

  • Target version changed from CoCoALib-0.99850 to CoCoALib-0.99880

Also available in: Atom PDF