用MATLAB实现IIF低通和高通滤波器的滤波特性，并让单位取样信号，周期方波信号和周期三角波信号通过IIF，验证IIR的滤波特性-IIF using MATLAB to achieve low-pass and high-pass filters filtering properties, and to allow units sampled signals, cycle square wave signal and the periodic triangular wave signal through the IIF, verify IIR filtering characteristics of