remez函数设计FIR低通滤波器
设计滤波器，使逼近低通滤波特性 。
要求通带波纹 ，阻带衰减 ，并用最小阶数实现。绘出设计的FIR数字滤波幅频特性曲线。
,remez function design FIR filter low-pass filter designed to approximate the low-pass filter characteristics. Requirements of passband ripple, stopband attenuation, and achieve a minimum order. Mapped the FIR digital filter design of amplitude-frequency characteristic curve.