## #243 factor FAILS on polynomial !!!

closed
nobody
5
2007-08-23
2003-03-03
No

Factor fails to factor a polynomial in two variables.

p:
(23*x^10*y^5 + 82*x^9*y^4 + 80*x^8*y^4 -
28*x^7*y^3 - 47*x^6*y^3 - 74*x^5*y^2 +
28*x^4*y^2 - 74*x^3*y + 25*x^2*y + 21*x - 41)
*
(78*x^10*y^5 + 49*x^9*y^4 + 48*x^8*y^4 +
49*x^7*y^3 + 65*x^6*y^3 - 8*x^5*y^2 +
82*x^4*y^2 - 7*x^3*y - 15*x^2*y - 6*x + 30)

factor(expand(p)) =&gt; irreducible

If this is some intentional limitation, it should give some
sort of warning. But I don't see why it should be.

This was a polynomial generated randomly using:

product(sum((random(200)-100) * x^i * y^entier(i/2),
i,0,10),
j,1,2)

Sometimes these polynomials factor correctly, but
mostly they come back as irreducible.

I tried setting Berlefact:false to see if that would make a
difference, but that causes an internal error
(POWERSET requires less than two arguments).

I also tried using rat instead of expand to make sure it
wasn't a multiplication problem rather than a factoring
problem.

Maxima version: 5.9.0
Maxima build date: 19:10 2/9/2003
host type: i686-pc-mingw32
lisp-implementation-type: Kyoto Common Lisp
lisp-implementation-version: GCL-2-5.0

## Discussion

• Barton Willis - 2003-03-04

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Macsyma 2.2 also fails to factor p after it has been
expanded. Setting berlefact : false didn't make any
difference.

Barton

• Stavros Macrakis - 2003-09-16

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Another factor failure:
(34*y^3+987*x*y-23*x^3-1)*(234*x^23*y^45-
978*x^43*y^10+1)
Setting berlefact:false gives error: POWERSET [or a callee]
requires less than two arguments.

• Stavros Macrakis - 2003-09-17

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Here is the smallest (degree and maximum product
coefficient) case I've been able to find:

(35*x*y^2+19*x^2+25) * (35*x*y^2+25*x^2+19)

Found by a combination of randomized and systematic
searching. The larger the coefficients, the denser the failure
cases.

Maxima 5.9.0 gcl 2.5.0 mingw32 W2k Athlon

• Robert Dodier - 2006-07-04
• labels: --> 460522

• Robert Dodier - 2006-09-09
• labels: 460522 --> Lisp Core - Polynomials

• Robert Dodier - 2006-09-09

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All three examples behave the same in Maxima 5.9.3cvs.

• Dan Gildea - 2007-08-08

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fixed in cvs.

incrlimk was not setting integer modulus big enough - removed buggy
logtwo and logn routines.

• Dan Gildea - 2007-08-08
• status: open --> pending

• SourceForge Robot - 2007-08-23

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This Tracker item was closed automatically by the system. It was
previously set to a Pending status, and the original submitter
did not respond within 14 days (the time period specified by
the administrator of this Tracker).

• SourceForge Robot - 2007-08-23
• status: pending --> closed

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