function [xdot] = sect_3_prob_5_J_ode_fn(t,x, c_1,c_2, omega_n,xi,x_1d)
%   
% Written by:
% -- 
% John L. Weatherwax                2006-08-28
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----

x_1 = x(1); 
x_2 = x(2); 

xdot = [ 0, 1 ; -omega_n^2, - 2*xi*omega_n ] * [ x_1; x_2 ] ...
     + [ 0; omega_n^2 ] * ( -c_1 * ( x_1 - x_1d ) - c_2 * x_2 );