function y_diff = prey(t,y)

global alpha beta;

y_1_init = y(1);
y_2_init = y(2);

y_1dot=y_1_init - alpha*y_2_init*y_1_init;
y_2dot=-y_2_init + beta*y_1_init*y_2_init;

y_diff=[y_1dot y_2dot]';