Newt_n(f_name, x0)

% Newt_n(f_name, x0) finds a root of a function by
% Newton iteration 
% f_name: the function name that defines the equation 
%         to solve
% x0: an initial guess.
% Copyright S. Nakamura, 1995
function x = Newt_n(f_name, x0)
x = x0; xb=x-999;
n=0;  del_x = 0.01;
while abs(x-xb)>0.000001
    n=n+1;   xb=x;
    if n>300 break; end
    y=feval(f_name, x);
    y_driv=(feval(f_name, x+del_x) - y)/del_x;
    x = xb - y/y_driv;
    fprintf(' n=%3.0f, x=%12.5e, y = %12.5e, ', n,x,y)
    fprintf(' yd = %12.5e \n', y_driv)
end
fprintf('\n     Final answer = %12.6e\n', x);