On May 7, 9:24 pm, John Cremona <john.crem...@gmail.com> wrote:
> Thanks for taking the time to explain, Jason.
>
> 2009/5/7 Jason Grout <jason-s...@creativetrax.com>:
>
>
>
>
>
> > John Cremona wrote:
> >> 2009/5/7 Nick Alexander <ncalexan...@gmail.com>:
> >>>> sage:RIF( 3 , 3.2 )
> >>>> 4.±1
> >>> -2 to unicode or whatever lets you type $\pm$.
>
> >>> As for the fact that 4.? is confusing to people who know nothing about
> >>> sage, that does not concern me in the slightest. I find lots of
> >>> things that I know nothing about confusing!
>
> >> Me too, but I have absolutely no idea why RIF(3,3.2) is anywhere near
> >> 4, so find this completely incomprehensible. Isn't it the interval
> >> from 3.0 to 3.2?
>
> >> I have never used the RIF, mainly because I cannot understand its output.
>
> > It's a compact notation for the interval:
>
> > [4.0-1 .. 4.0+1] = [3.0 .. 5.0]
>
> > The question mark just means the interval goes from the number with last
> > digit minus one to the number with last digit plus one.
>
> > For example:
>
> > 3.5? is the interval [3.4 .. 3.6]
>
> > 3.293948? is the interval [3.293947 .. 3.293949]
>
> > More documentation can be found by taking any element x of RIF and doing
> > x.str?
>
> > You can change the default back to printing an explicit interval by doing:
>
> > sage: sage.rings.real_mpfi.printing_style='brackets'
> > sage: RIF(3,3.2)
> > [3.0000000000000000 .. 3.2000000000000002]
> > sage: sage.rings.real_mpfi.printing_style='question'
> > sage: RIF(3,3.2)
> > 4.?
>
> Why is this not 3.1? From what you said earlier that means the
> interval between 3.1-0.1=3 and 3.1+0.1=3.2, doesn't it?
>
> John
>
I think it's because 3.2 is not exact in base 2, and thus the value we
have is just slightly greater than 3.2,
(you can see it a few lines above: 3.2000000000000002)
Yann
>
> > Carl, could you comment on the difference between these two cases?
>
> > sage: RIF(3,3.199999999999999)
> > 3.1?
> > sage: RIF(3,3.1999999999999999)
> > 4.?
>
> > Thanks,
>
> > Jason
>
> > --
> > Jason Grout
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