在matlab下实现信号频谱分析：利用快速付里叶变换FFT得到下列信号的频谱，并绘制信号及频图形：1.长2s的方波信号，频率f=10Hz -In matlab signal spectrum analysis: the fast in leaf transform FFT get pay of spectrum, the signal and drew the signal and frequency graphics: 1. The long 2s, frequency f = squar