Jacobi iteration what the wrong of my code please help

% jacobi Method
 clc
 clear
 format short
 A=[2.08 -1 0 0;-1 2.08 -1 0;0 -1 2.08 -1;0 0 -1 2.08];
 b=[200.0 0.8 0.8 40.8];
 l=tril(-A,-1);
 u=triu(-A,1);
 d=diag(diag(A));
 tj=inv(d)*(l+u);
 cj=inv(d)*b;
 xj=[1;1;1];
 N=5;
 for i=1:N
   xj=tj*xj+cj;
 [i xj'] 
end

Answer 1

[Walter Roberson]

size(d) is 4 x 4, so size(inv(d)) is 4 x 4.

size(b) is 1 x 4.

You cannot use matrix multiplication * operator between a 4 x 4 and a 1 x 4. The second dimension of the first operand (4 here) must match the first dimension of the second operand (1 here)

[Walter Roberson]

By the way, with the way you construct d, you can be sure that inv(d) is diag(1./diag(A))

[ayah zaghlol]

Ok Thank you I want to solve this matrix for n of iterations how?

A=[2.08 -1 0 0;-1 2.08 -1 0;0 -1 2.08 -1;0 0 -1 2.08]; b=[200.0 0.8 0.8 40.8];

[Walter Roberson]

I do not understand what you are asking for?