Re: Re: warning for Round[Log[2]/Log[4]]

*To*: mathgroup at smc.vnet.net*Subject*: [mg13950] Re: [mg13940] Re: warning for Round[Log[2]/Log[4]]*From*: "George E. Hrabovsky" <georgeh at hep.physics.wisc.edu>*Date*: Fri, 11 Sep 1998 15:06:40 -0400*Sender*: owner-wri-mathgroup at wolfram.com

When I do Log[2]/Log[4]//N I get 0.5, when I do Log[2]/Log[4]//N//Round I get 0. George ---------- > From: Ronald Bruck <bruck at math.usc.edu> To: mathgroup at smc.vnet.net > To: mathgroup at smc.vnet.net > Subject: [mg13950] [mg13940] Re: warning for Round[Log[2]/Log[4]] > Date: Tuesday, September 08, 1998 1:52 AM > > In article <6ssvo6$m9r at smc.vnet.net>, > Wouter Meeussen <eu000949 at pophost.eunet.be> wrote: > >** this is not a bug report *** > > Windows 3.0.0.0. > > > [That Mathematica didn't have enough precision to compute Round[Log[2]/Log[4]] > > Hmmm. Interesting. Since Log[2]/Log[4] = 1/2, Mathematica can't decide > whether to round up or down--it SHOULD apply round-to-even, to give > zero, but it's trying to do this with just numerical values. > > As I recall, deciding when A == B is a profoundly difficult problem. > I'm not sure how else one could go about this. (Oh, sure, the > immediate problem could be fixed by applying a special rule for > logarithms, but what about special functions for which the relations > are still undiscovered?) > > --Ron Bruck