function [b,a,nu]=z_mult(b1,a1,n1,b2,a2,n2)
%	[b,a,nu]=z_mult(b1,a1,n1,b2,a2,n2)
% G(z)=H1(z)*H2(z)
	b=conv(b1,b2);
	a=conv(a1,a2);
	nu=n1+n2;