Function: poldisc
Section: polynomials
C-Name: poldisc0
Prototype: GDn
Help: poldisc(pol,{v}): discriminant of the polynomial pol, with respect to main
 variable if v is omitted, with respect to v otherwise.
Description:
 (gen):gen        poldisc0($1, -1)
 (gen, var):gen   poldisc0($1, $2)
Doc: discriminant of the polynomial
 \var{pol} in the main variable if $v$ is omitted, in $v$ otherwise. Uses a
 modular algorithm over $\Z$ or $\Q$, and the \idx{subresultant algorithm}
 otherwise.
 \bprog
 ? T = x^4 + 2*x+1;
 ? poldisc(T)
 %2 = -176
 ? poldisc(T^2)
 %3 = 0
 @eprog

 For convenience, the function also applies to types \typ{QUAD} and
 \typ{QFI}/\typ{QFR}:
 \bprog
 ? z = 3*quadgen(8) + 4;
 ? poldisc(z)
 %2 = 8
 ? q = Qfb(1,2,3);
 ? poldisc(q)
 %4 = -8
 @eprog
