Le mardi 19 avril 2016 à 22:10 -0700, Jeffrey Sarnoff a écrit :
> Hi,
>
> You have discovered that IEEE standard floating point numbers have
> two distinct zeros: 0.0 and -0.0. They compare `==` even though they
> are not `===`. If you want to consider +0.0 and -0.0 to be the same,
> use `==` or `!=` not `===` or `!==` when testing floating point
> values (the other comparisons <=, <, >=, > treat the two zeros as a
> single value).
There's actually an open issue about what to do with -0.0 and NaN in
Dicts: https://github.com/JuliaLang/julia/issues/9381
It turns out it's very hard to find a good solution.
Regards
> > Hello everyone!
> > I was wondering if the following behavior of round() has an special
> > purpouse:
> >
> > a = round(0.1)
> > 0.0
> >
> > b = round(-0.1)
> > -0.0
> >
> > a == b
> > true
> >
> > a === b
> > false
> >
> > bits(a)
> > "0000000000000000000000000000000000000000000000000000000000000000"
> >
> >
> > bits(b)
> > "1000000000000000000000000000000000000000000000000000000000000000"
> >
> > So the sign stays around...
> >
> > I am using this rounded numbers as keys in a dictionary and julia
> > can tell the difference.
> >
> > For example, I expected something like this:
> > dict = [i => exp(i) for i in [a,b]]
> > Dict{Any,Any} with 1 entry:
> > 0.0 => 1.0
> >
> > but got this:
> > dict = [i => exp(i) for i in [a,b]]
> > Dict{Any,Any} with 2 entries:
> > 0.0 => 1.0
> > -0.0 => 1.0
> >
> > It is not a big problem really but I would like to know where can
> > this behaviour come handy.
> >
> > Cheers!
> >
