方法一:Gauss列主元消去法
function [x]=gauss(A,b)
n=size(A,1);x=zeros(n,1);
for k=1:n-1
%looking for column max anSEO靠我d exchange rows
Max=abs(A(k,k));MaxIndex=k;
for u=k+1:n
if(abs(A(u,k))>Max)
MaxIndex=u;Max=abs(A(u,k));
eSEO靠我nd
end
if Max==0
disp(This matrix can not be solved by Gauss algorithm);
end
Atemp=A(MaxIndex,:);btemp=b(SEO靠我MaxIndex);
A(MaxIndex,:)=A(k,:);b(MaxIndex)=b(k);
A(k,:)=Atemp;b(k)=btemp;
%diagonalization
for i=k+1:n
MSEO靠我ik=A(i,k)/A(k,k);b(i)=b(i)-Mik*b(k);
for j=k+1:n
A(i,j)=A(i,j)-Mik*A(k,j);
end
end
end
%solving
x(n)=b(n)/ASEO靠我(n,n);
for i=n-1:-1:1
x(i)=(b(i)-A(i,i+1:n)*x(i+1:n))/A(i,i);
end
end方法二:Jacobi迭代
function [x]=jacobi(A,bSEO靠我,x0,e)
D=diag(diag(A));L=tril(A,-1);U=triu(A,1);
B=-D\(L+U);f=D\b;
if max(abs(eig(B)))>=1
x=Jacobi methoSEO靠我d can not converge;
else
x=B*x0+f;
while norm(x-x0)>=e
x0=x;
x=B*x0+f;
end
end
end方法三:Gauss-Seidel迭代
functionSEO靠我 [x]=gs(A,b,x0,e)
D=diag(diag(A));L=tril(A,-1);U=triu(A,1);
B=-(D+L)\U;f=(D+L)\b;
if max(abs(eig(B)))>=SEO靠我1
x=Guass-Seidel method can not converge;
else
x=B*x0+f;
while norm(x-x0)>=e
x0=x;
x=B*x0+f;
end
end
end附:不使用SEO靠我DLU分解的迭代算法
function [x]=jacobi_nodlu(A,b,x0,e,N)
D=diag(diag(A));L=tril(A,-1);U=triu(A,1);
B=-D\(L+U);fSEO靠我=D\b;
if max(abs(eig(B)))>=1
x=Jacobi method can not converge;
else
n=size(A,1);x=zeros(n,1);k=0;
while kSEO靠我
for i=1:n
if i==1
x(1)=(b(1)-A(1,2:n)*x0(2:n))/A(1,1);
elseif i==n
x(n)=(b(n)-A(n,1:n-1)*x0(1:n-1))/A(n,SEO靠我n);
else
x(i)=(b(i)-A(i,1:i-1)*x0(1:i-1)-A(i,i+1:n)*x0(i+1:n))/A(i,i);
end
end
if norm(x-x0)
break;
end
x0=xSEO靠我;k=k+1;
end
if k==N
disp(迭代次数已到达上限!);
end
disp([迭代次数 k=,num2str(k)])
end
endfunction [x]=gs_nodlu(A,b,x0,e,SEO靠我N)
D=diag(diag(A));L=tril(A,-1);U=triu(A,1);
B=-(D+L)\U;f=(D+L)\b;
if max(abs(eig(B)))>=1
x=Guass-SeidelSEO靠我 method can not converge;
else
n=size(A,1);x=zeros(n,1);k=0;
while k
for i=1:n
if i==1
x(1)=(b(1)-A(1,2:n)SEO靠我*x0(2:n))/A(1,1);
elseif i==n
x(n)=(b(n)-A(n,1:n-1)*x(1:n-1))/A(n,n);
else
x(i)=(b(i)-A(i,1:i-1)*x(1:i-1SEO靠我)-A(i,i+1:n)*x0(i+1:n))/A(i,i);
end
end
if norm(x-x0)
break;
end
x0=x;k=k+1;
end
if k==N
disp(迭代次数已到达上限!);
endSEO靠我
disp([迭代次数 k=,num2str(k)])
end
end使用范例:
clear
clc
%set the problem
A=[2,-2,-1;
4,1,-2;
-2,1,-1];
b=[-2;1;-3];SEO靠我
disp(answer for Q1);
%guass method
x=gauss(A,b);
disp(Guass method:x=);disp(x);
%jacobi method & gs methSEO靠我od
x0=[0;0;0];e=1e-3;
x=jacobi(A,b,x0,e);
disp(Jacobi method:x=);disp(x);
N=100;x=jacobi_nodlu(A,b,x0,e,SEO靠我N);
disp(Jacobi method:x=);disp(x);
x=gs(A,b,x0,e);
disp(Guass-Seidel method:x=);disp(x);
N=100;x=gs_nodSEO靠我lu(A,b,x0,e,N);
disp(Guass-Seidel method:x=);disp(x);%set the problem
A=3*eye(100)-circshift(eye(100),SEO靠我1)-circshift(eye(100),-1);A(1,100)=0;A(100,1)=0;
b([1:100],1)=1;b(1,1)=2;b(100,1)=2;
disp(answer for QSEO靠我2);
%guass method
x=gauss(A,b);
disp(Guass method:x=);disp(x);
%jacobi method & gs method
x0=zeros(100,1)SEO靠我;e=1e-4;
x=jacobi(A,b,x0,e);
disp(Jacobi method:x=);disp(x);
N=100;x=jacobi_nodlu(A,b,x0,e,N);
disp(JacoSEO靠我bi method:x=);disp(x);
x=gs(A,b,x0,e);
disp(Guass-Seidel method:x=);disp(x);
N=100;x=gs_nodlu(A,b,x0,e,SEO靠我N);
disp(Guass-Seidel method:x=);disp(x);
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