On 8 November 2016 at 10:17, Thierry Dumont <tdum...@math.univ-lyon1.fr> wrote: > Le 08/11/2016 à 08:43, Vincent Delecroix a écrit : >> Concerning representation of algebraic numbers, it is printed as an >> exact rational if and only if it is stored as an exact rational. It >> will be if the method exactify has been called on the underlying >> representation of the number. Here is a simple example that shows the >> difference >> > > Ha, yes... > > But I am not sure to understand. > > sage: y=QQbar(cos(pi/18)) > sage: y.radical_expression() > 1/4*(4*(1/128*I*sqrt(3) + 1/128)^(1/3) + 1)/(1/128*I*sqrt(3) + 1/128)^(1/6) > > ok! good! > > sage: y > 0.9848077530122081? + 0.?e-18*I > > ok. > sage: y.imag() > 0.?e-18 > sage: y.imag() == 0 > True > I accept this as 0 is "in" 0.?e-18 > > Now: > > sage: y.exactify() > sage: y > 0.9848077530122081? + 0.?e-18*I > > raaahhh ! grrr !
This is *not* a rational!! We might want to special case the representation of real numbers of QQbar. I opened https://trac.sagemath.org/ticket/21838 for that purpose. Vincent -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To post to this group, send email to sage-support@googlegroups.com. Visit this group at https://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/d/optout.
