function vprime = odeplay(t,vin)

global c;
global m;
%global b;
global k;


x = vin(1);
y = vin(2);

% compute derivatives for predator-prey model
% from K Tung p. 166

%xprime = x-2*x*y%.1*x; %x-2*y;
%yprime = x*y-y; %-y; %3*x - 4*y;

% nonlinear pendulum

% xprime = y%.1*x; %x-2*y;
% yprime = -(k/m)*sin(x) -(c/m)*y; %-y; %3*x - 4*y;

% Strogatz ex 6.3.2, p. 153 (Here Strogatz's a = c)

xprime = -y + c*x*(x^2 + y^2);
yprime = x + c*y*(x^2 + y^2);

% map back to vector format
vprime=[xprime;yprime];

end