function [bz,az] = zmapping(bZ,aZ,Nz,Dz)
% 從Z域到z域的頻帶變換
% -------------------------------------------------------
% [bz,az] = zmapping(bZ,aZ,Nz,Dz)
% 實(shí)現(xiàn):
%          b(z)   b(Z)|
%          ---- = ----|     N(z)
%          a(z)   a(Z)|@Z = ----
%                           D(z)
%
bzord = (length(bZ)-1)*(length(Nz)-1);
azord = (length(aZ)-1)*(length(Dz)-1);

bz = zeros(1,bzord+1);
for k = 0:bzord
    pln = [1];
    for l = 0:k-1
        pln = conv(pln,Nz);
    end
    pld = [1];
    for l = 0:bzord-k-1
        pld = conv(pld,Dz);
    end
    bz = bz+bZ(k+1)*conv(pln,pld);
end

az = zeros(1,azord+1);
for k = 0:azord
    pln = [1];
    for l = 0:k-1
        pln = conv(pln,Nz);
    end
    pld = [1];
    for l = 0:azord-k-1
        pld = conv(pld,Dz);
    end
    az = az+aZ(k+1)*conv(pln,pld);
end

az1 = az(1); az = az/az1; bz = bz/az1;