%直接三角分解法（1） function x,y,L,U=nalu(a,b) n=length(a); x=zeros(n,1);y=zeros(n,1); U=zeros(n,n);L=eye(n,n); U(1,:)=a(1,:); L(2:n,1)=a(2:n,1)/U(1,1); for k=2:nU(k,k:n)=a(k,k:n)-L(k,1:k-1)*U(1:k-1,k: n);L(k+1:n,k)=(a(k+1:n,k)-L(k+1:n,1:k-1)*U (1:k-1,k)/U(k,k); end for i=2:n y(1,1)=b(1,1);y(i,1)=b(i,1)-L(i,1:i-1)*y(1:i-1,1); end y(:,1); for i=n-1:-1:1 x(n,1)=y(n,1)/U(n,n);x(i,1)=(y(i,1)-U(i,i+1:n)*x(i+1:n,1)/U (i,i); end x(:,1);clear all;clc; A=1,2,3;2,5,2;3,1,5; b=14;18;20; x,y,L,U=nalu(A,b);function x,y,L,U=sanjiao(a,b) n=length(a); x=zeros(n,1); y=zeros(n,1); L=eye(n,n); U=zeros(n,n);%L,U U(1,:)=a(1,:); L(2:n,1)=a(2:n,1)/U(1,1); for j=2:nU(j,j:n)=a(j,j:n)-L(j,1:j-1)*U(1:j-1,j: n);L(j+1:n,j)=(a(j+1:n,j)-L(j+1:n,1:j-1)*U (1:j-1,j)/U(j,j); end %Ux=y,Ly=b y(1,1)=b(1,1); for i=2:ny(i,1)=b(i,1)-L(i,1:i-1)*y(1:i-1,1); endx(n,1)=y(n,1)/U(n,n); for i=n-1:-1:1x(i,1)=(y(i,1)-U(i,i+1:n)*x(i+1:n,1)/U (i,i); endclear all; a=1,2,3;2,5,2;3,1,5; b=14;18;20; x,y,L,U=sanjiao(a,b); x y