Re: [Help-glpk] glp_mip_col_val is returning negative zero

[Michael Hennebry]

On Fri, 1 May 2015, Andrew Makhorin wrote:

> On Fri, 2015-05-01 at 15:17 +0000, Agostina Kodelia wrote:
> > Hi!
> >  I'm solving a very simple postman travelling problem with
> > the glp_intopt method. When I retrieved the column value
> > with glp_mip_col_val, it returns a negative zero. The zero is alright,
> > but I don't understand why has a minus, could anyone explain to me why
> > is this happening?
>
> This is because the IEEE 754 standard which most of modern FPUs conform
> to claims that a floating-point zero has the sign bit. A negative zero
> may appear, for example, on computing (2. - 3.) * (5. - 5.) = -1. * +0.
> = -0.

The minus sign was not actually necessary.
C89 is not required to notice the sign of zero.
That printf did suggests that its author made a special effort.
So far as I know,
none of C89's successors are required to notice the sign of zero.
C99 implementations *may* choose to honor IEEE floating point
and to note the fact in a C99-defined preprocessor symbol.
C99 defines said choice to include noticing the sign of zero.

--
Michael   address@hidden
"SCSI is NOT magic. There are *fundamental technical
reasons* why it is necessary to sacrifice a young
goat to your SCSI chain now and then."   --   John Woods