Changes in polynomial quotient ring are intended?

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Jörg-Volker

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Dec 19, 2018, 2:11:25 PM12/19/18
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Hi,

in version 8.4 this example doesn't work anymore as it did at least until version 8.2:
varl = ['x0', 'x1', 'x2', 'x3']
B
= BooleanPolynomialRing(names = varl)
B
.inject_variables(verbose=False)
P
.<p> = PolynomialRing(B)
Byte.<t> = P.quotient_ring( p^4 + p + 1 )
X
= B.gens()
x
= Byte(list(X))
E
= x^2
print( E )
type
(Byte)

Previously the outcome was
x3*t^3 + (x1 + x3)*t^2 + x2*t + x0 + x2
<class 'sage.rings.polynomial.polynomial_quotient_ring.PolynomialQuotientRing_generic_with_category'>
so the result of `x^2` is also in the quotient ring. In version 8.4 I see
x3*t^6 + x2*t^4 + x1*t^2 + x0
<class 'sage.rings.quotient_ring.QuotientRing_generic_with_category'>
If this change in behaviour is intended how would I have to modify my example in order to get the same results as before?

Regards, Jörg.

Nils Bruin

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Dec 20, 2018, 12:49:38 PM12/20/18
to sage-devel
On Wednesday, December 19, 2018 at 11:11:25 AM UTC-8, Jörg-Volker wrote:
Hi,

in version 8.4 this example doesn't work anymore as it did at least until version 8.2:
varl = ['x0', 'x1', 'x2', 'x3']
B
= BooleanPolynomialRing(names = varl)
B
.inject_variables(verbose=False)
P
.<p> = PolynomialRing(B)
Byte.<t> = P.quotient_ring( p^4 + p + 1 )

Given that in 8.4 we now have

sage: t^4+t+1 == 0
False

I think we have a fairly critical bug.

John H Palmieri

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Dec 20, 2018, 1:12:36 PM12/20/18
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Notice by the way:

sage: (t^4 + t + 1).is_zero()
True
sage: (t^4 + t + 1).__nonzero__()
False
sage: t^4 + t + 1 != 0
True

So something is working, but clearly not everything.

Emmanuel Charpentier

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Dec 20, 2018, 2:38:06 PM12/20/18
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I agree that this seems a critical bug. Would you mind filing a ticket with importance "critical" ?

Jörg-Volker

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Dec 21, 2018, 12:10:03 PM12/21/18
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On Thursday, December 20, 2018 at 8:38:06 PM UTC+1, Emmanuel Charpentier wrote:
I agree that this seems a critical bug. Would you mind filing a ticket with importance "critical" ?

 There is this ticket : https://trac.sagemath.org/ticket/26929 which seems to me relevant. Should I open another one anyway?

Regards, Jörg.

Nils Bruin

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Dec 21, 2018, 1:13:13 PM12/21/18
to sage-devel
On Friday, December 21, 2018 at 9:10:03 AM UTC-8, Jörg-Volker wrote:

 There is this ticket : https://trac.sagemath.org/ticket/26929 which seems to me relevant. Should I open another one anyway?

That ticket already tracks and references the issue discussed here. No other ticket is required.
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