function [x,k]=tridiag(n)
    v1 = ones(n-1,1);
    v2 = 3*ones(n,1);
    A = diag(v1,-1)+diag(v2,0)+diag(v1,1);
    b = ones(n,1);
    [x,k]=gausseidel(A,b,1e-12,10,ones(n,1));
endfunction