function vprime = predprey(t,vin)

global r;
global a;
global b;
global k;


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

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

xprime = r*x - a*x*y;
yprime = b*x*y - k*y;

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

end