Bill Page wrote: > On Thu, May 14, 2009 at 4:59 AM, John Cremona wrote: >> This debate has been going on for as long as computers have been in >> existence. Yes, there is a case to be made the odd roots of negative >> reals should return a negative real instead of the "principal" complex >> root. But that leads to more subtle problems in other places. > > Granted. Choose your poison. > >> If all of mathematica, maple and matlab do the "non-obvious thing" >> there must be a good reason for it! > > There is but I think these reasons do not necessarily apply to Sage. > >> And as Mike said, you can always get the >> real root by inserting brackets. >> > > ??? > > Consider the problem to define > > f(x) = x^(1/3) > > so that it takes the real branch for x < 0. The best I have been able > to come up with so far is: > > sage: f = lambda x: RealField(53)(x).sign()*(RealField(53)(x).sign()*x)^(1/3) > sage: plot(f,(-2,2)) >
plot(lambda x: RR(x).nth_root(3), -5, 5, plot_points=20) This is from a mailing list discussion last year (Feb 2008?) on the same issue. In fact, there have been several discussions of this. Search sage-devel for "plotting cube roots", for example. I thought the above plot was in the faq, but I can't find it now. Jason --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
