No, these aren't subnormal values, although they are small. Using %.16e
does print them all accurately though, so that's a bit misleading. By
"hang" I meant that it doesn't return quickly, not that it won't ever
return.
On Wed, Nov 5, 2014 at 2:27 PM, Tamas Papp <tkp...@gmail.com> wrote:
> I think that you are just running floats which are "subnormal" in a
> fixed-point decimal representation: with "%.17f", they have (on average)
> a single 0 after the decimal dot, with "%.18f", they have two,
> etc. Printing them with %f but a fixed number of digits is not the right
> way, since you waste digits on these zeroes.
>
> It should not hang at 21, except, of course, it will
> take more time to generate a float below approx 1e-5.
>
> David's issue is different, and essentially boils down to
>
> julia> bits(1/Inf)
> "0000000000000000000000000000000000000000000000000000000000000000"
>
> julia> bits(-1/Inf)
> "1000000000000000000000000000000000000000000000000000000000000000"
>
> which are equal when compared with == (which follows the IEEE standard)
> but not is(,) (which compares bits).
>
> Best,
>
> Tamas
>
> On Wed, Nov 05 2014, Stefan Karpinski <ste...@karpinski.org> wrote:
>
> > This code prints a random Float64 that requires more than 15 digits to
> > reconstruct:
> >
> > while true
> > x = rand()
> > if parsefloat(@sprintf("%.15f", x)) != x
> > println(x)
> > break
> > end
> > end
> >
> >
> > There are lots of them. What's more surprising is that if you replace 15
> > with anything up to 20, it still returns really quickly – at 21 it hangs.
> > This implies that values requiring up to 20 digits to print "honestly"
> are
> > quite common.
> >
> > On Wed, Nov 5, 2014 at 1:53 PM, David van Leeuwen <
> > david.vanleeu...@gmail.com> wrote:
> >
> >> I couldn't resist this after my cholfact() revelation...
> >>
> >> On Wednesday, November 5, 2014 11:23:03 AM UTC+1, Stefan Karpinski
> wrote:
> >>>
> >>> Well, I'm not sure what the intention was, but this fact is true: for
> >>> floating-point values x and y of the same type, x == y is true if and
> only
> >>> if string(x) == string(y).
> >>>
> >>>
> >> julia> a = inv(eye(2))
> >>
> >> 2x2 Array{Float64,2}:
> >>
> >> 1.0 -0.0
> >>
> >> 0.0 1.0
> >>
> >> julia> a[1,2] == a[2,1]
> >>
> >> true
> >>
> >> julia> string(a[1,2]) == string(a[2,1])
> >>
> >> false
> >> (pardon the formatting, I don't seem to have a good handle on this in
> >> google groups)
> >>
> >> Cheers,
> >>
> >> ---david
> >>
>
>
