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Topic: Is it me or is it Wolfram?
Replies: 16   Last Post: May 13, 2013 4:51 PM

 Messages: [ Previous | Next ]
 JT Posts: 1,448 Registered: 4/7/12
Re: Is it me or is it Wolfram?
Posted: May 10, 2013 1:40 PM

On 10 Maj, 19:13, Ray Vickson <RGVick...@shaw.ca> wrote:
> On Thursday, May 9, 2013 11:01:54 AM UTC-7, JT wrote:
> >http://www.wolframalpha.com/input/?i=0.499999999999999999999999999999...
>
> > n = -1.
>
> > 0.49999999999999999999999999999999999999999 = (n/2-1)/n
>
> >http://www.wolframalpha.com/input/?i=%3D%2810000000000000000000000000...
>
> > 0.49999999999999999999999999999999999999999=(100000000000000000000000000000000000000000/2-1)/
>
> > 100000000000000000000000000000000000000000
>
> > I do not understand to, can please someone explain why and how wolfram
>
> > get -1 for the upper calculation, it is obvious using the one below
>
> > what the solution is?
>
> > And if there was two solutions should not Wolfram give them both? What
>
> > is going on here, i am total newb to math calculators so tell me what
>
> > is going on?
>
> It must have something to do with truncation of floating-point numbers. I do not have access to Mathematica, but here is your example in Maple 14:
>
>   eq:=z=(n/2-1)/n: lprint(eq);   z = (1/2*n-1)/n  <---equation
>   Nz:=solve(eq,n): lprint(Nz);   -2/(2*z-1) <--- solution
>
> Default digits setting = 10 gives:
> eq1:=0.49999999999999999999999999999999999999999 = (n/2-1)/n :
> lprint(eq1); .49999999999999999999999999999999999999999 = (1/2*n-1)/n
> solve(eq1,n);
>                                          42
>                           0.1000000000 10
> (this is 0.10e42)
> subs(z=0.49999999999999999999999999999999999999999,Nz);
>                            Float(-infinity)
>
> Even with the low digits setting, Maple handles the direct equation well, but fails when the parameter is
> substituted into the solution (because the extra digits are handled in one problem but not in the other)'
>
> Now let's increase the digits setting:
>
> Digits:=60;
> subs(z=0.49999999999999999999999999999999999999999,Nz);
>                                                                   42
>  0.100000000000000000000000000000000000000000000000000000000000 10
> (this is 0.100....00 e42)
>
> Now both ways handle the extra digits well enough to yield identical answers.
>
> I presume something like this happens also in Mathematica. However, if by "Wolfram" you mean wolfram alpha, I don't know if it allows you to change digit settings easily.

And just one more thing, for all the prostitutes in mathematics go
fuck yourself.

Date Subject Author
5/9/13 JT
5/9/13 JT
5/9/13 JT
5/10/13 JT
5/10/13 JT
5/10/13 RGVickson@shaw.ca
5/10/13 JT
5/10/13 JT
5/10/13 JT
5/10/13 LudovicoVan
5/10/13 JT
5/10/13 LudovicoVan
5/10/13 JT
5/10/13 JT
5/12/13 JT
5/13/13 JT
5/13/13 Brian Q. Hutchings