The expression -0.0 means the floating point number that in memory has the
same
bit representation as 0.0, but the sign bit set to 1. One can see this
applying
the 'bits' function to 0.0 and -0.0.
I seem to remember that the IEEE floating point convention says that for
`sqrt(-0.0)` the sign bit has to be reset, so that
julia> sqrt(-0.0)
-0.0
would be wrong while MATLAB, R,... returning 0.0 are correct.
The expression -0.0 means the floating point number that in memory has the
same
bit representation as 0.0, but the sign bit set to 1. One can see this
applying
the 'bits' function to 0.0 and -0.0.
I seem to remember that the IEEE floating point convention says that for
`sqrt(-0.0)` the sign bit has to be reset, so that
julia> sqrt(-0.0)
-0.0
would be wrong while MATLAB, R,... returning 0.0 are correct.
For `1/-Inf` the sign bit is not reset because this expression should be
the
limit of 1/-x for very large numbers x, i.e. approaching 0 from left.
On Friday, December 19, 2014 12:13:57 PM UTC+1, Tamas Papp wrote:
>
> Hmmm, did you read the whole blog post, including the update at the end?
> Julia does handle signed zeroes correctly when working with floats.
>
> As to what signed zeros "mean" -- they have some applications, including
> indicating the direction of underflow. Probably you don't need to worry
> about them much since 0.0 == -0.0 (unless you specifically want to use
> them).
>
> I usually think about -0.0 as equivalent to 0.0 except for +, -, *, and
> /, especially when Inf is involved. Thinking about it as some limit is
> not very intuitive for IEEE floats, eg
>
> julia> log(-0.0)
> -Inf
>
> julia> sqrt(-0.0)
> -0.0
>
> all of which are correct IEEE.
>
> Best,
>
> Tamas
>
>
> On Fri, Dec 19 2014, cdm <[email protected] <javascript:>> wrote:
>
> > i stumbled across a post and got to wondering what Julians thought of it
> ...
> >
> > http://www.walkingrandomly.com/?p=5152
> >
> >
> > the author presents the case that Python is not IEEE compliant, but
> > MATLAB is and Julia is close:
> >
> > "From the wikipedia page on Division by Zero
> > <http://en.wikipedia.org/wiki/Division_by_zero>: *“The IEEE 754
> > standard specifies that every floating point arithmetic operation,
> > including division by zero, has a well-defined result”.*
> >
> >
> > the author reports that in Julia
> >
> > julia> 1/(-0)
> > Inf
> >
> >
> > but MATLAB "correctly" returns -Inf ...
> >
> >
> > i am not sure that signed zero (-0)
> > means anything to me ...
> >
> > should it?
> >
> > many thanks,
> >
> > cdm
>
