function [X,Y,L,U]=chase(A,B)
% 追赶法求解三对角方程组

%  NUMERICAL METHODS: Matlab Programs
% (c) 2007 by Xie Liling
%  Complementary Software to accompany the textbook:
%  Information and Computing Science: A Laboratory Course

% 追
L=eye(size(A));
U=zeros(size(A));
U(1,1)=A(1,1);
L(2,1)=A(2,1)/A(1,1);
n=length(A(:,1));
for i=1:n-1
    U(i,i+1)=A(i,i+1);
end
for i=2:n
    L(i,i-1)=A(i,i-1)/U(i-1,i-1);
    U(i,i)=A(i,i)-L(i,i-1)*A(i-1,i);
end

Y=zeros(size(B));
Y(1)=B(1);
for i=2:n
    Y(i)=B(i)-L(i,i-1)*Y(i-1);
end

% 赶
X=zeros(size(B));
X(n)=Y(n)/U(n,n);
for i=n-1:-1:1
    X(i)=(Y(i)-U(i,i+1)*X(i+1))/U(i,i);
end