说明：  我自己写的求二维矩阵的标准方差函数，因为本人毕设需要用到，可是在Matlab中我没有找到合适的函数，所以亲自写了一个，希望对一些朋友有用
(I wrote it myself for two-dimensional matrix of standard deviation function, because I completed the set up needed, but in Matlab, I did not find a suitable function, so personally wrote a hope for some useful Friend)