Bill Allombert on Sun, 01 Aug 2010 19:59:47 +0200 |
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Re: Real zero in libpari |
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.