Re: qflllgram

[Gonzalo Tornaria <tornaria@math.utexas.edu>]

On Mon, Feb 27, 2006 at 12:58:22PM -0500, Igor Schein wrote:
> On Mon, Feb 27, 2006 at 01:34:11AM -0500, Gonzalo Tornaria wrote:
> > ? qflllgram([1,0;0,-1],0)
> >   *** qflllgram: the PARI stack overflows !
> 
> I also have a question stemming from this behavior.  Is the first
> argument a valid input?  It's definitely symmetric, but does it
> correspond to a positive definite quadratic form, like the manual
> requires?

It is certainly not definite, since it has a +1 and a -1 in the
diagonal (numbers in the diagonal are always represented).

The point is that running qflllgram with an /integer/ indefinite
matrix uses a lot of memory (unbounded?) and it doesn't complete. If
you replace any of the diagonal entries by its corresponding floating
point number, the exception comes back immediately, and the same goes
if you use flag=1 (lllgramint).

Best, Gonzalo