Gauss-Seidal solver for 1D heat equation

I tried using Gauss-Seidal solver by computing A and the right hand side. But still got an error:) asking for help.

 x_min= 0;
x_max = 1;
N = 10; 
lamda=15;
L = x_max-x_min; 
h = L/N; 
x = linspace(x_min,x_max,N+1)';
uexact= @(x) 8*(x-3*x.^2+4*x.^3-2*x.^4);
% uexact= @(x) 4*(x-x.^2);
% f = @(x) 8*lamda*ones(1,N-1); % Source term 
f = @(x) 48*lamda*(2*x-1).^2;
u_exact = uexact(x); 
ua = uexact(x_min); 
ub = uexact(x_max);
u = zeros(N-1,1); 
A = zeros(N-1,N-1); 
b = f(x(2:N)); %
b(1) = b(1) + ua/h^2; 
for i=2:N-1
  b(i) = b(i) + ub/h^2;
end
A1 = diag( 2*ones(1,N-1) );
A2 = diag( -1*ones(1,N-2), 1 ); 
A3 = diag( -1*ones(1,N-2), -1 ); 
A = (A1 + A2 + A3);
A = lamda*A/h^2;
x0=zeros(N-1,1);
tol=0.0001;
M=1000000;
k=1;
x2=x0;
while(k<M)
  n = length(b);
  x2(1)=(b(1)-A(1,2)*x0(2)-A(1,3)*x0(3))/A(1,1);
for j = 2 : n
   x2(j)=(b(j)-A(j,1:j-1).*x2(1:j-1)-A(j,j+1:n).*x0(j+1:n))./A(j,j);
end
  x1=x2';
  error=abs(x1(j))-x0;
  if norm(error)< tol%if norm(x1-x0)< tol
       disp('succefful');
      break  
    end
end    
plot(x,x1)

[John D'Errico]

What was your error? Did it generate garbage numbers that cannot be meaningful? Was there an actual error message? What?

By not telling us what you think is wrong, you force us to run your code, then guess why you think there is a problem.

If there was an error, provide the COMPLETE text of the error message. EVERYTHING that was in red.

[Dereje]

The is the error: In an assignment A(:) = B, the number of elements in A and B must be the same. In line:

     x2(j)=(b(j)-A(j,1:j-1).*x2(1:j-1)-A(j,j+1:n).*x0(j+1:n))./A(j,j);

[Torsten]

x2(j)=(b(j)-A(j,1:j-1)*x2(1:j-1)-A(j,j+1:n)*x0(j+1:n))/A(j,j);

[Dereje]

The error is gone but it's running inside the loop.

[Dereje]

I fixed it now. Thanks!