Igor Schein on Tue, 19 Jan 1999 13:30:44 -0500


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Re: nfgaloisconj() bug


On Tue, Jan 19, 1999 at 06:56:36PM +0100, Karim BELABAS wrote:
> 
> > Also, I noticed another thing, that goes back at least as far as
> > 2.0.11:
> > 
> > ? nfgaloisconj(nfinit(x^4-2*x^2+9),0)
> > [x, 1/3*x^3 - 2/3*x, -1/3*x^3 + 2/3*x, -x]
> > ? nfgaloisconj(nfinit(x^4-2*x^2+9),2)
> > [x, 0, 0, -x]
> > 
> > Correct me if I'm wrong, but from reading documentation, I don't see a
> > reason why the output should depend on the flag.  Or are these 2
> > output isomorphic to each other?
> 
> There's a difficult precision problem here. None of the generic nfgaloisconj
[snip]

Interesting to note that nfgaloisconj(nfinit(x^4-2*x^2+9),2) returns
correct output only at \p9 or less ( 9 significant digits ).  With 19
or more significant digits, it doesn't.  Are you planning to tune that
up eventually?  Is it do-able in general?

Thanks
Igor