说明：  设计一个滤波器滤除正弦信号中的噪声，还原正弦信号。正弦信号为sin100t，噪声信号是均值为0、方差为1的高斯白噪声。信号采样频率为2000 Hz。
(The design of a filter to filter out the noise in the sinusoidal signal, restoring the sinusoidal signal. Sinusoidal signal sin100t, and noise signal with mean 0 and variance 1 Gaussian white noise. Signal sampling frequency of 2000 Hz.)