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1、判断时不变系统举例,例:判断下列系统是否为时不变系统? (1) yzs(k) = f (k) f (k 1) (2) yzs (t) = t f (t) (3) y zs(t) = f ( t),解 (1) 令g (k) = f(k kd) T0, g (k) = g(k) g (k 1) = f (k kd) f (kkd 1 ) 而 yzs (k kd) = f (k kd) f (kkd 1) 显然 T0,f(k kd) = yzs (k kd) 故该系统是时不变的。,判断时不变系统举例,例:判断下列系统是否为时不变系统? (1) yzs(k) = f (k) f (k 1) (2) y
2、zs (t) = t f (t) (3) y zs(t) = f ( t),解 (2) 令g (t) = f(t td) , T0, g (t) = t g (t) = t f (t td) 而 yzs (t td)= (t td) f (t td) 显然T0,f(t td) yzs (t td) 故该系统为时变系统。,(3) y zs(t) = f ( t) 令g (t) = f(t td) , T0,g (t) = g ( t) = f( t td) 而 yzs (t td) = f ( t td),显然 T0,f(t td) yzs (t td) 故该系统为时变系统。,直观判断方法: 若f ()前出现变系数,或有反转、展缩变换,则系统为时变系统。,