Re: Real zero in libpari

[Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>]

On Sun, Aug 01, 2010 at 05:33:50PM +0200, Karim Belabas wrote:
> * Bill Allombert [2010-07-26 15:14]:
> > On Mon, Jul 26, 2010 at 02:35:04PM +0200, Jeroen Demeyer wrote:
> > > Hello pari-users,
> > > 
> > > I have a technical question about the t_REAL type.  The documentation
> > > says that real zero is characterized by having the sign equal to zero.
> > > My question is: does a real zero NEED to have lg == 2 in order to be a
> > > valid GEN?
> > 
> > Currently, yes. This is necessary because z[2] must be normalized, and so
> > cannot be 0. Thus the only possibility is that z[2] does not exist i.e. lg=2.
> 
> A real 0 is allowed to have an arbitrary length, otherwise functions
> like affsr() make no sense --  as currently implemented, documented, and
> used (look for affsr(0,.) in the PARI sources.

Ah, sorry for spreading misinformation. So it only works in the other way: 
only a real zero can have lg = 2.

Cheers,
Bill.