Function: algmul
Section: algebras
C-Name: algmul
Prototype: GGG
Help: algmul(al,x,y): element x*y in al.
Doc: Given two elements $x$ and $y$ in \var{al}, computes their product $xy$
 in the algebra~\var{al}.
 \bprog
 ? A = alginit(nfinit(y), [-1,-1]);
 ? algmul(A,[1,1,0,0]~,[0,0,2,1]~)
 %2 = [2, 3, 5, -4]~
 @eprog

 Also accepts matrices with coefficients in \var{al}.
