Hi, Using math.log has a disadvantage; it is less accurate.
sage: print n(math.log(2),100) sage: print n(log(2),100) 0.69314718055994528622676398300 0.69314718055994530941723212146 Rolandb On 30 aug, 06:48, Robert Bradshaw <rober...@math.washington.edu> wrote: > On Aug 29, 2009, at 12:44 PM, Rolandb wrote: > > > > > > > On 29 aug, 18:43, John H Palmieri <jhpalmier...@gmail.com> wrote: > >> On Aug 29, 8:51 am, Simon King <simon.k...@nuigalway.ie> wrote: > > >>> Note that expon uses Maxima, because you use the logarithm. So, I > >>> reckon that your problem is related withhttp://trac.sagemath.org/ > >>> sage_trac/ticket/4731 > >>> andhttp://trac.sagemath.org/sage_trac/ticket/6818. > >>> If not, you might try to work around by thinking what "expon" really > >>> does. For example, one of my first problems with Sage occurred > >>> when I > >>> used the logarithm for determining the number of digits of a natural > >>> number n -- len(str(n)) is much faster! > > >> Or you can use "math.log" instead of "log" -- this should use the > >> Python log function rather than the Maxima one: use > > >> def expon(mx,g): return floor(math.log(mx)/math.log(g))+1 > > >> John > > > Hi, > > > The whole issue boils down to: > > > floor(log(256)/log(2))+1 > > > which takes 'ages' to compute (Sage 4.1). > > > print floor(ln(256)/ln(2))+1 is no improvement; floor(math.log(mx)/ > > math.log(g))+1 is. > > Ah, that makes sense. It is numerically computing this to higher and > higher precision, trying to figure out whether or not it is greater > than or less than 8. Of course, you can't do this with high precision > arithmetic, so eventually it gives up. > > What we should do is also try to check to see if it is exactly equal > to an integer symbolically before computing out too far...maybe even > do both in parallel. > > sage: bool(log(256)/log(2) == 8) > True > > - Robert --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
