function (ans)=Newton (fun, a, count, e) 
% this function is used for solving the equation root; 
% by Newton iteration method, f is the target equation, a is the starting point, the count for the maximum number of iterations, e for accuracy; 
Syms x; 
Df=diff (fun (x)); 
X0=a; 
For (I=1: count) 
X1=x0 - fun (x0)/subs (df, x0); 
If (abs (x1 - x0) & gt; E) 
X0=x1; 
End 
End 
Ans=x0; 

 error using sym/subsindex (line 825) 
Invalid indexing the or function definition. Indexing must follow indexing. The MATLAB function the arguments must be 
-- the variables, and the function body must be sym expression. 

Newton error (line 5) 
Df=diff (fun (x));