www.pudn.com > MATLABpro.rar > qgauss.m

%a=[0.012,0.01,0.167;1,0.8334,5.91;3200,1200,4.2]; 
%b=[0.6781,12.1,981]'; 
a=[1,-1,2,-1;2,-2,3,-3;1,1,1,0;1,-1,4,3];%系数矩阵a 
b=[-8,-20,-2,4]'; 
%a=[0.003000,59.14;5.291,-6.130];%系数矩阵a1 
%b=[59.17,46.78]'; 
L=[1,2,3,4]; 
n=length(b); 
clu=[]; 
for k=1:n-1 
    [p,q]=find(abs(a)==max(max(abs(a(k:n,k:n))))); 
     
    if(p~=k|q~=k) 
      t=a(k,:); 
      a(k,:)=a(p,:); 
      a(p,:)=t; 
      r=a(:,k); 
      a(:,k)=a(:,q); 
      a(:,q)=r; 
      t=L(k);L(k)=L(q);L(q)=t; 
      u=b(k); 
      b(k)=b(p); 
      b(p)=u; 
    end 
    m(k+1:n,k)=a(k+1:n,k)./a(k,k); 
    a(k+1:n,k:n)=a(k+1:n,k:n)-m(k+1:n,k)*a(k,k:n); 
    b(k+1:n)=b(k+1:n)-m(k+1:n,k)*b(k);     
end 
 
 
%%%%%%%%%%%%%回代%%%%%%%%%%% 
y(n)=b(n)/a(n,n); 
for i=n-1:-1:1 
    sum=0; 
    for j=i+1:n 
        sum=sum+a(i,j)*y(j); 
    end 
    y(i)=(b(i)-sum)/a(i,i); 
end 
 
x(L(n))=y(n); 
x(L(1:n-1))=y(1:n-1); 
jie=x'