基于傅里叶级数的信号分解编写一个matlab函数，参数有：脉高、脉宽、余弦信号项数。该函数使用指定项数的余弦信号来逼近（合成）指定的矩形脉冲信号，计算并返回有限项逼近时合成波形与实际矩形脉冲信号的均方误差值。-Based on Fourier series of signal decomposition write a matlab function, the parameters are: pulse height, width, number of items cosine signal. This function uses a cosine signal to approximate the specified number of items (synthetic) specified rectangular pulse signal, calculates and returns the mean square error and the actual value of the composite waveform of the rectangular pulse signal is limited entry approach.