Changes in polynomial quotient ring are intended?

[Jörg-Volker]

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]

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]

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]

I agree that this seems a critical bug. Would you mind filing a ticket with importance "critical" ?

[Jörg-Volker]

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]

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.