Re: Re: Re: algebraic numbers
- To: mathgroup at smc.vnet.net
- Subject: [mg106246] Re: [mg106220] Re: [mg106192] Re: algebraic numbers
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Wed, 6 Jan 2010 05:59:02 -0500 (EST)
- References: <200912290620.BAA02732@smc.vnet.net> <hhpl0g$9l1$1@smc.vnet.net> <201001050647.BAA24123@smc.vnet.net> <E44EA2F2-1274-43E8-93DE-DC5BD31884A5@mimuw.edu.pl> <op.u52ai6jwtgfoz2@bobbys-imac.local>
Well, you are obviously misunderstanding what I am trying to explain but I have no desire to spend any more time on it. I give up. Perhaps you should try to explain yourself why Mathematica gives In[1]:= Element[1.2, Rationals] Out[1]= False In[2]:= Element[1.2, Reals] Out[2]= True and you might also read http://en.wikipedia.org/wiki/Computable_number (but that's the last time I posting anything to do with any logic or mathematics here.) Andrzej Kozlowski On 5 Jan 2010, at 22:31, DrMajorBob wrote: > RandomReal[] returns numbers from a countable set of rationals. > > Or call them reals, if you must; it still selects from a countable set of possibilities... not from the uncountable unit interval in the reals. > > The range of RandomReal[] is a set of measure zero, just like the algebraic numbers. > > Bobby > > On Tue, 05 Jan 2010 02:08:24 -0600, Andrzej Kozlowski <akoz at mimuw.edu.pl> wrote: > >> >> On 5 Jan 2010, at 15:47, DrMajorBob wrote: >> >>> If computer reals are THE reals, why is it that RandomReal[{3,4}] can >>> never return Pi, Sqrt[11], or ANY irrational? >> >> It can't possibly do that because these are computable real numbers the set of computable real numbers if countable and has measure 0. Computable numbers can never be the outcome of any distribution that selects numbers randomly from a real interval. >> >> The most common mistake people make about real numbers is to think that numbers such as Sqrt[2] or Pi as being in some sense typical examples of an irrational number or a transcendental number but they are not. They are very untypical because they are computable: that is, there exists a formula for computing as many of their digits as you like. But we can prove that the set of all reals with this property is countable and of measure 0. So Sqrt[2] is a very untypical irrational and Pi a very untypical transcendental. So what do typical real look like? Well, I think since a "typical" real is not computable we cannot know all of its digits and we cannot know any formula for computing them. But we can know a finite number of these digits. So this looks to me very much like the Mathematica concept of Real - you know a specified number of significant digits and you know that there are infinitely many more than you do not know. It seems to me the most natural way to think about non-computable reals. >> >> Roger Penrose, by the way, is famous for arguing that our brain is somehow able to work with non-computable quantities, although of course not by using digital expansions. But this involves quantum physics and has been the object of a heated dispute since the appearance of "The emperor's New Mind". >> > > > -- > DrMajorBob at yahoo.com
- References:
- Re: Re: algebraic numbers
- From: DrMajorBob <btreat1@austin.rr.com>
- Re: Re: algebraic numbers