id summary reporter owner description type status priority milestone component version resolution keywords cc
259 Bug with genus normal.lib gorzel pfister "
Here I consider a smooth and absolutely irreducible elliptic curve {f=0}
As its genus is 1,
the genus of the union of this elliptic curve with any rational curve is 0.
But normal::genus does not compute this correctly.
The problem seems to be that factors x,y are not treated correctly.
{{{
> ring r=0,(x,y),dp;
> poly f = x6y4+4x5y3+3x4y3+6x4y2+19/3x3y2+4x3y+3x2y2+11/3x2y+x2+2xy+1/3x+y;
> genus(f);
1 // OK
> genus((x+y)*f);
0 // OK since x+y=0 has genus zero
> genus(x*f);
The given polynomial is zero! // Message from hnoether.lib
1 // Wrong, should give 0 again
> genus(y*f);
The given polynomial is zero!
1 // Also false
> genus(y*x);
-1 // This, for the two rational components, is correct
> TRACE = 1;
> genus(x*f);
entering pre_HN (level 4)
The given polynomial is zero!
leaving pre_HN (level 4)
}}}
" bug closed major 3-2-0 and higher singular-libs 3-1-6 fixed pfister