function [b,a]=ladr2dir(K,C)

% 極點－零點Lattice結(jié)構(gòu)到直接型結(jié)構(gòu)的轉(zhuǎn)換
% ------------------------------------------------------------------------------
% [b,a]=ladr2dir(K,C)
% b=直接型的分子多項式系數(shù)
% a＝直接型的分母多項式系數(shù)
% K=格型系數(shù)(反射系數(shù)),[K1,K2,...,KN]
% C=梯形系數(shù),[C1,C2,...,CN]
% ------------------------------------------------------------------------------

N=length(K);
M=length(C);
C=[C,zeros(1,N-M+1)];
J=1;
a=1;
A=zeros(N,N);
for m=1:1:N
    a=[a,0]+conv([0,K(m)],J);
    A(m,1:m)=-a(2:m+1);
    J=fliplr(a);
end
b(N+1)=C(N+1);
for m=N:-1:1
    A(m,1:m)=A(m,1:m)*C(m+1);
    b(m)=C(m)-sum(diag(A(m:N,1:N-m+1)));
end