设定a为N(0,1)的500个随机数和i长为500，以n=8、16、64.分别调用u_pcm.m ，从中计算量化误差f=a-a_quan并绘图，分别输出各样值的量化误差图形。 -Set a for the N (0,1) of 500 random numbers and i long for the 500 to n = 8,16,64. Were called u_pcm.m, quantization error from the calculation of f = a-a_quan