function A=GenA(n)
%L=round(rand(n,n)*10-5);
%U=round(rand(n,n)*10-5);
L=rand(n,n)*100-50;
U=rand(n,n)*100-50;
for i=1:n
    for j=1:(i-1)
        L(i,j)=0;
    end
    for j=(i+1):n
        U(i,j)=0;
    end
    while U(i,i)==0
       U(i,i)=round(rand(1)*10-5);
    end
    L(i,i)=1;
end
A=L*U;


function x=Gauss(A,b)
n=length(A);
A
for j=1:n
    for i=(j+1):n
        if A(i,j)~=0
            b(i,1)=b(i,1)-b(j,1)*A(i,j)/A(j,j);
            A(i,1:n)=A(i,1:n)-A(j,1:n)*A(i,j)/A(j,j);
        end
    end
end
b;
U=A
for i=n:-1:1
    for j=(i+1):n
        b(i,1)=b(i,1)-x(j,1)*U(i,j);
    end
    x(i,1)=b(i,1)/U(i,i);
end


n=30;
A=GenA(n);
x=rand(n,1)*10;
b=A*x;
x2=Gauss(A,b)
x
x2-x
norm=((x2-x)'*(x2-x))^(1/2)