% 6.581 PS4
% Problem 1
% newton.m

function [x, e, flag] = newton(func, x0, tol, maxItr)

% Implements Newton's method.  The arguments to this function are as 
% follows:
% 
% func   - is a vector function of x.  The return value of func is the time
%          derivative of x evaluated at x and the jacobian evaluated at x.
%          For example:
%            function [dxdt, dxdx] = myfun(x)
%               dxdt = -x^2;
%               dxdx = -2*x;
% x0     - is the initial guess
% tol    - the error tolerance.  When the two norm of func(x) is below tol 
%          the function will return
% maxItr - the maximum number of steps before the method gives up.  If this
%          happens then the error flag will be set to 0;
%
% Returns:
%
% x      - If successfull this is the the root of the function
% e      - The residual error.  This is the two norm of func(x)
% flag   - 1 if the method met the error tolerance.  0 otherwise. 
%
% You will have to fill in the missing lines of code labled with
% %% CHANGE ME

i = 1
x = x0

[f, fp] = func(x)
e       = norm(f)

while(e > tol && i < maxItr)
    dx = ; %% CHANGE ME %% 
    x  = x + dx; 
    [f, fp] = func(x);
    e = norm(f);
    i = i + 1
end;

if(e > tol)
    flag = 0;
else
    flag = 1;
end