function [xdot] = sect_4_prob_2_J_ode_fn(t,x, u0,x0,n,a,b,c)
%   
% 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.
% 
%-----

n = length(x); 
xdot = zeros(n,1); % x = [ lambda(t), x(t) ]

lambda = x(1); 
x      = x(2); 

u       = sect_4_prob_2_u_from_x_N_lambda( t, x, lambda, u0,x0,n,a,b,c );
xdot(1) = a*lambda + (n/x0) * ( 1 - exp( - u/u0 ) ) * ( ( x / x0 )^(n-1) ) * exp( - c * t );
xdot(2) = -a * x + b * u;