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*To*: "Alex Shinn" <alexshinn@xxxxxxxxx>*Subject*: Re: infinities reformulated*From*: "Chongkai Zhu" <mathematica@xxxxxxxxx>*Date*: Tue, 31 May 2005 15:16:37 +0800*Cc*: "srfi-70" <srfi-70@xxxxxxxxxxxxxxxxx>*Delivered-to*: srfi-70@xxxxxxxxxxxxxxxxx

======= At 2005-05-31, 09:59:56 Alex Shinn wrote: ======= >On 5/31/05, Chongkai Zhu <mathematica@xxxxxxxxx> wrote: >> >> And your statement "the precision of an inexact (or exact) number >> representation cannot be unlimited" is wrong. For example, Mathematica >> implements "unlimited precision number", although it may have some >> flaws. > >It cannot be "unlimited" in the sense that it is at least memory limited. >No matter how much memory you have, you can never exactly represent >the square root of 2 with a floating point representation - that is the >definition of irrational, you don't even need to go to transcendental numbers >for this. In fact, irrational literally means "no ratio," and was only later >applied by analogy to imply a lack of reasoning. Yes, there is memory limited. But here the "unlimited" should mean the implementation makes no limit on how big the number will be. Just as many Scheme implementations provide "unlimited" big integer. I mentioned Mathematica, only for the "inexact number" part of it, not the "symbolic manipluation" part of it. For example, if you want to save the square root of 2 as an inexact number, you can write: v1=1.414 the precision or the inexact number v1 is 4 (decimal digits); but you can also write v2=1.414213562373095048801688724209698078569671875376948073176679737990732478462107038850387534327641573 and v2 will get precision 100 (all these digits are saved into memory). > v1^2 1.9994 > v2^2 2.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 > >But your original statement was "arbitrarily big," not "unlimited," and this >should be allowed. Infinity in this case could be defined as the range of >all real numbers greater than the largest possible BigFloat using all of >memory for the exponent. > >-- >Alex = = = = = = = = = = = = = = = = = = = = Chongkai Zhu mathematica@xxxxxxxxx 2005-05-31

**Follow-Ups**:**Re: infinities reformulated***From:*Aubrey Jaffer

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