function [K,C]=dir2ladr(b,a)

% 直接型結(jié)構(gòu)到極點(diǎn)－零點(diǎn)Lattice結(jié)構(gòu)轉(zhuǎn)換
% ------------------------------------------------------------------------------
% [K,C]=dir21adr(b,a)
% K=格型系數(shù)(反射系數(shù)),[K1,K2,...,KN]
% C=梯形系數(shù),[C1,C2,...,CN]
% b=直接型的分子多項(xiàng)式系數(shù)
% a＝直接型的分母多項(xiàng)式系數(shù)
% ------------------------------------------------------------------------------

a1=a(1);
a=a/a1;
b=b/a1;
M=length(b);
N=length(a);
if M>N
    error('***向量b的長度必須<=向量a的長度***')
end
b=[b,zeros(1,N-M)];
K=zeros(1,N-1);
A=zeros(N-1,N-1);
C=b;
for m=N-1:-1:1
    A(m,1:m)=-a(2:m+1)*C(m+1);
    K(m)=a(m+1);
    J=fliplr(a);
    a=(a-K(m)*J)/(1-K(m)*K(m));
    a=a(1:m);
    C(m)=b(m)+sum(diag(A(m:N-1,1:N-m)));
end