设计一个Chebyshev II型低通滤波器，指标如下： 通带边界频率：，通带最大衰减：。 阻带截止频率：，阻带最小衰减：。-Design a II Chebyshev type low pass filter, the index is as follows: Pass band boundary frequency: 0.2pi, pass band attenuation: 1db. Stop band cutoff frequency: 0.4pi, minimum at

butterworth 低通滤波器的实现ButterWorth滤波器的低通、高通、带通、带阻功能。-Low pass filter to achieve low pass, high pass, band pass, band stop function of ButterWorth filter.

巴特沃思低通、高通、带通、帯阻滤波器以及切比雪夫高通、低通、带通、帯阻滤波器。(Butterworth low-pass, high pass, band-pass and band stop filter, Chebyshev low-pass, high pass, band-pass and band stop filter.)