I can't find where my mistake is?

A=[1 2 -1; 2 2 -1; 2 5 2];
b=[3; 4; 2];
x=[1; 1; 1];
tol=1e-7;
d=diag(A);
X=ones(3,1);
r=ones(3,1);
while norm(r)/norm(X)>=tol                 
    X=(b-A*x)./d+x;     
    r=X-x;
    x=X;
end
X
%X should be 1 4/9 -10/9

[Bob Thompson]

It seems like your system is unstable, as X just perpetually increases in value. Without knowing the equation you're trying to code I don't know that I can help much more than that, but I would look at the X value equation some more.

Answer 1

[Takumi]

In the Jacobi method, matrix 'A' must be diagonally dominant.