Re: [sage-devel] Problem of reduction of rational functions
On 16 April 2018 at 00:06, Nils Bruin wrote: > On Sunday, April 15, 2018 at 3:53:08 PM UTC-7, Dima Pasechnik wrote: >> >> >> It would be nice to have better simplification rules for QQ (and more >>> generally fraction fields). >>> >> >> I suppose it's only OK to have as an option, as in general computing such >> a canonical >> form would be slow, no? >> >> For fraction fields of euclidean domains it's not so bad (as > ZZ['x'].fraction_field() shows). Furthermore, if you consistently don't > clear common content from your numerator/denominator pairs you can end up > with quite bad coefficient blow-up. > > Of course, the work-around is to use Z['x'].fraction_field(). > In this case (one variable, over QQ) it would be simple to extract the leading coefficients of the numerator and denominator, say a and b, reduce the rational number a/b to a1/b1, and scale the rational function so that the new leading coefficients are a1 and b1 which will be coprime integers. This is simpler than writing numerator and denominator as a rational times a primitive integral polynomial, though that is probably what users would prefer. John > -- > You received this message because you are subscribed to the Google Groups > "sage-devel" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sage-devel+unsubscr...@googlegroups.com. > To post to this group, send email to sage-devel@googlegroups.com. > Visit this group at https://groups.google.com/group/sage-devel. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
Re: [sage-devel] Problem of reduction of rational functions
in multivariate case things like GCD are certainly very expensive. -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
Re: [sage-devel] Problem of reduction of rational functions
On Sunday, April 15, 2018 at 3:53:08 PM UTC-7, Dima Pasechnik wrote: > > > It would be nice to have better simplification rules for QQ (and more >> generally fraction fields). >> > > I suppose it's only OK to have as an option, as in general computing such > a canonical > form would be slow, no? > > For fraction fields of euclidean domains it's not so bad (as ZZ['x'].fraction_field() shows). Furthermore, if you consistently don't clear common content from your numerator/denominator pairs you can end up with quite bad coefficient blow-up. Of course, the work-around is to use Z['x'].fraction_field(). -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
Re: [sage-devel] Problem of reduction of rational functions
On Sunday, April 15, 2018 at 9:27:40 PM UTC+1, vdelecroix wrote: > > The representation is indeed not canonical but the object compare > coherently > > sage: R.=QQ[] > sage: (2*t+2)/(2*t) > (2*t + 2)/(2*t) > sage: (2*t+2)/(2*t) == (t+1)/t > True > > The reason is that 2 is a unit in QQ. You can compare with > > sage: R.=ZZ[] > sage: (2*t+2)/(2*t) > (t + 1)/t > > It would be nice to have better simplification rules for QQ (and more > generally fraction fields). > I suppose it's only OK to have as an option, as in general computing such a canonical form would be slow, no? Dima > > Vincent > > On 15/04/2018 21:37, dhr wrote: > > Hi > > > > Reduction of rational functions seems not to work in specific cases. > > In the following output, > > > > === > > sage: R.=QQ[] > > sage: (2*t+2)/(2*t) > > (2*t + 2)/(2*t) > > sage: (2*t+2)/(2) > > t + 1 > > sage: (2*t^2+2*t)/(2*t) > > t + 1 > > > > === > > 2 is not reduced in the first calculation. > > > > SageMath version 8.1 > > > -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
Re: [sage-devel] Problem of reduction of rational functions
The representation is indeed not canonical but the object compare coherently sage: R.=QQ[] sage: (2*t+2)/(2*t) (2*t + 2)/(2*t) sage: (2*t+2)/(2*t) == (t+1)/t True The reason is that 2 is a unit in QQ. You can compare with sage: R.=ZZ[] sage: (2*t+2)/(2*t) (t + 1)/t It would be nice to have better simplification rules for QQ (and more generally fraction fields). Vincent On 15/04/2018 21:37, dhr wrote: Hi Reduction of rational functions seems not to work in specific cases. In the following output, === sage: R.=QQ[] sage: (2*t+2)/(2*t) (2*t + 2)/(2*t) sage: (2*t+2)/(2) t + 1 sage: (2*t^2+2*t)/(2*t) t + 1 === 2 is not reduced in the first calculation. SageMath version 8.1 -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
