function [dx] = pop(t,y)
  
  alpha = 0.1;
  beta = 2.0;
  gamma = 4.0;
  delta = 0.4;
  
  dx(1) = alpha*y(1)*y(2) - beta*y(1);
  dx(2) = beta*y(2) - delta*y(1)*y(2);
  
  dx = dx.';
endfunction