Oscillator (unstable fixed point y x>0 x>0 少<0 y>0 x<0 0 <0 XOscillator (unstable fixed point) 0 0 > > y x & & 0 0 > < y x & & 0 0 < > y x & & 0 0 < < y x & & x& = 0 y& = 0 ufp y x 6