 　　利用fft()进行快速傅立叶变换，得到频谱，画出正弦函数及其频谱

 　　找出频谱中使得Y轴取最大值时的估计频率记为ft

 　　加入白噪声，绘出信噪比和均方误差的关系曲线

-　using fft () for fast Fourier transformation, spectrum, to draw the sine function and its spectrum　　find the spectrum makes the Y-axis maximum value when the estimated frequency is denoted by ft　　adding white noise, SNR plot and mean square error curve