That answers it perfectly!
On Thursday, January 14, 2016 at 1:00:00 PM UTC-8, Nils Bruin wrote:
>
> On Thursday, January 14, 2016 at 12:36:32 PM UTC-8, Matthias Goerner wrote:
>>
>>
>> # Lift polynomial back to Q[x][y]
>> lifted = factor.map_coefficients(lambda c:Rx(c.lift()), Rxy)
>>
>> Are you sure this is what you want and what you did before? The
> documentation of map_coefficients says that the second argument is to be
> the new *base ring*. Indeed, with your code I get:
>
> sage: parent(lifted)
> Univariate Polynomial Ring in y over Univariate Polynomial Ring in y over
> Univariate Polynomial Ring in x over Rational Field
>
> i.e., an element in the polynomial ring QQ[x][y][Y], where "Y" is really
> "y", (which is difficult to distinguish from the previous "y" visually ,
> but sage does distinguish them).
>
> Hence:
>
> sage: parent(val)
> Univariate Polynomial Ring in y over Univariate Polynomial Ring in x over
> Real Interval Field with 53 bits of precision
>
> (who knows which y was substituted or was used before ... You could figure
> it out if you wanted).
>
> If instead you do:
>
> sage: lifted=factor.map_coefficients(lambda c:Rx(c.lift()), Rx)
> sage: val = lifted.substitute(x = RIF(-2.67512520581, -2.67512520582), y =
> RIF(.00001, 1.00002))
> sage: type(val)
> <type 'sage.rings.real_mpfi.RealIntervalFieldElement'>
>
> I don't think there are any issues.
>
> Incidentally, the whole "x=var('x')" thing is making things unnecessarily
> complicated. You'd be better off setting them to the appropriate values
> right away:
>
> Rx.<x>=PolynomialRing(RationalField(),'x')
> Rxy.<y>=PolynomialRing(Rx,'y')
>
> Or you could use
>
> x=Rx.0
> y=Rxy.0
>
>
>> Something has changed. Was I using it incorrectly and this improved or is
>> this a regression?
>>
>
> Yes, according to the documentation (which presumably hasn't changed
> between your old version an 6.10), you were using something that shouldn't
> result in what you apparently were trying to obtain.
>
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