中文说明：第一额程序为模拟产生一个正态随机序列X(n)，画出产生的随机序列波形、相关函数（与理论曲线对比） 和功率谱密度。第二个程序为产生一个信号X(n)，绘出信号及其幅度频谱曲线，当中心频率向左搬移f0＝200Hz时，求出其低通等效信号，并绘出其幅度频谱、信号的同相、正交分量及包络。当中心频率向左搬移f0＝100Hz时，求出其低通等效信号，并绘出其幅度频谱、信号的同相、正交分量及包络。
English Description：
First program for simulating a random sequence x (n), draw random sequence of waveforms, the correlation function (compared with the theoretical curves)And power spectral density. The second program to produce a signal x (n), sketch of signals and their spectra, when center frequency when moving f0=200Hz to the left, to find out the low-pass equivalent signal, and draw its amplitude spectrum, signal phase and quadrature components and envelope. When the Centre frequency when moving f0=100Hz to the left, to find out the low-pass equivalent signal, and draw its amplitude spectrum, signal phase and quadrature components and envelope.