On Jan 16, 2008, at 9:25 AM, Carl Witty wrote: > On Jan 15, 9:23 pm, Robert Bradshaw <[EMAIL PROTECTED]> > wrote: >> I was under the impression that MPFR was supposed to give identical >> answers across all platforms (unlike, say, RDF). I was wondering if >> any experts in the area could explain the numerical noise in cases >> like >> >> http://sagetrac.org/sage_trac/ticket/1790 >> >> Is this something to be worried about, or are MPFR results not truly >> platform independent? > > Computations done only with MPFR/MPFI should definitely be platform > independent. However, p.roots(ring=CIF) is done by first finding the > roots numerically (using either numpy or Pari, depending on the > precision), and then verifying/refining the roots using MPFI. The > initial numpy or Pari roots may differ across platforms, so the MPFI > refinement may also give different results. (I believe that the > results are always correct, though, in that the returned intervals do > always include the real root.) > > I don't know how to make the results platform-independent without > writing a lot of code (and possibly slowing down root-finding > significantly).
Ah... This completely answers my question. Thanks. - Robert --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://sage.scipy.org/sage/ and http://modular.math.washington.edu/sage/ -~----------~----~----~----~------~----~------~--~---
