Re: Re: warning for Round[Log[2]/Log[4]]
- To: mathgroup at smc.vnet.net
- Subject: [mg13955] Re: [mg13940] Re: warning for Round[Log[2]/Log[4]]
- From: BobHanlon at aol.com
- Date: Fri, 11 Sep 1998 15:06:45 -0400
- Sender: owner-wri-mathgroup at wolfram.com
As you indicated, the problem occurs because numerical values are used in attempting to evaluate the ratio. However, Log[2]/Log[4] // Simplify Log[2]/Log[4] %//FullSimplify 1/2 Consequently, Round[Log[2]/Log[4]//FullSimplify] 0 Bob Hanlon In a message dated 9/8/98 5:06:18 AM, bruck at math.usc.edu wrote: >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?)