function [sys, x0] = simdopi2(t, x, u, flag);
%系統描述
   if abs(flag) == 1
   	sys(1) = u(1);
   	sys(2) = x(1);
   elseif abs(flag) == 0
   	sys=[2,0,0,1,0,0]; x0 = [0; -1];
   else
   	sys = [];		
   end