Function: algb
Section: algebras
C-Name: algb
Prototype: mG
Help: algb(al): the element b of the center of the cyclic algebra al used
 to define it.
Doc: Given a cyclic algebra $\var{al} = (L/K,\sigma,b)$ output by
 \tet{alginit}, returns the element $b\in K$.
 \bprog
 nf = nfinit(y);
 ? p = idealprimedec(nf,7)[1];
 ? p2 = idealprimedec(nf,11)[1];
 ? A = alginit(nf,[3,[[p,p2],[1/3,2/3]],[0]]);
 ? algb(A)
 %5 = Mod(-77, y)
 @eprog
