function zd = foo(t,z)
  alpha = 0.1;
  beta = 2.0;
  delta = 0.4;
  gamma = 4.0;
  
  x = z(1,:);
  y = z(2,:);
  xd = alpha*x - beta*x.*y;
  yd = -delta*y + gamma*x.*y; 
  zd = [xd;yd];
  
% zd(1,:) = alpha*z(1,:);
% zd(2,:) = -delta*z(2,:);
endfunction