symbolic newton method for nonlinear equations.

I have written this code to get a function handle matrix of a system of equations and a guess vector yet when I run it it returns obsolete answers.surprisingly,when I try to debug it,the first iteration goes as planned yet it fails afterwards.

I would be happy if you told me what is wrong with my code and how to fix it.

thank you in advance.

ps:my vwersion of matlab is 2013b

function [x,varargout] = newton_solve(f,x0,varargin)
k = 1000;
epsilon = 10^-3;
i = 0;
if ~isempty(varargin)
    for i = 1:length(varargin) - 1
        switch varargin{i}
            case('k')
                k = varargin(i + 1);
            case('epsilon')
                epsilon = varargin(i + 1);
        end
    end
end
xlast = x0';
sol = x0;
varsmat = sym('x',[1,length(x0)]);
vars = {};
xlastin = {};
for i = 1:length(varsmat)
    vars{i} = varsmat(i);
    xlastin{i} = x0(i);
end
j = jacobian(f(vars{:}));
while true
    nj=doubl(subs(j,vars,mat2cell(xlast')));
    in = inv(nj);
    i = i + 1;
    temp = transpose(f(xlastin{:}));
    debug_check = in * temp;
    sol = xlast - debug_check;
    xlast = sol;
    if i>k || norm(sol) < epsilon
        break
    end
    
end
x = sol;

[VBBV]

   nj=double(subs(j,vars,mat2cell(xlast'))) % typo

It seems you have a typo error in while loop.