function [xdot] = sect_5_prob_6_ode_fn(t,x, T1,T2,xair,xd,k1,k2,c1,c2)
%   
% Checked on 2011-12-06 (no errors found)
% 
% 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 = [ x1(t), x2(t), lambda_1(t), lambda_2(t) ]

x1       = x(1); 
x2       = x(2);
lambda_1 = x(3); 
lambda_2 = x(4); 

xdot(1) = -(x1 - xair)/T1 + k1*(x2-x1) - ( k2^2 / (2*c2) )*lambda_1;
xdot(2) = -(x2 - xair)/T2 + k1*(x1-x2);
xdot(3) = ( 1/T1 + k1 )*lambda_1            - k1*lambda_2 - 2*c1*( x1 - xd );
xdot(4) =          - k1*lambda_1 + ( 1/T2 + k1 )*lambda_2 - 2*c1*( x2 - xd );