将处于矩阵对角处的两点用最少的像素连接起来

输入：

mat_in：为二值矩阵，为1的点在对角线处

输出：连接后的矩阵-　In the matrix are connected at two corners with a minimum of input pixels　up: after the connection matrix:　mat_in: a binary matrix, at a point at the diagonal output