function yp = van_der_pol_eq(x,t,params)
% VAN_DER_POL_EQ - returns dy/dt for the Van Der Pol equation
%   
% 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.
% 
%-----

a = params(1);
b = params(2);
c = params(3); 

yp = zeros(2,1);
yp(1) = x(2);
yp(2) = -a*(1-x(1)*x(1))*x(2) - b*x(1) + c;