说明：  利用双线性Z变换设计巴特沃斯和切比雪夫I型IIR数字滤波器，包括低通、高通、带通、带阻四种形式。使用者只需指定通带、阻带的边缘实际频率及相应的衰减，便可输出数字滤波器 的级联形式的各子系统分子、分母的系数，并输出其幅频和相频响
(Bilinear Z transform design Butterworth and Chebyshev Type I IIR digital filters, including low pass, high pass, band pass, band stop four forms. Users simply specify the passband edge frequency stopband actual and corresponding attenuation subsystems can form molecular cascade output digital filter coefficients of the denominator, and the output of its magnitude and phase frequency response)