ON THE CONSTRUCTION OF NORMAL MIXED DIFFERENCE MATRICES
标准混合差集矩阵的构造

By exploring the relationship between difference matrices and orthogonal decomposition of projection matrices, this paper presents a general method for constructing smaller normal mixed difference matrices. Moreover, given a normal mixed difference matrix of order $r+1$ and a difference matrix of order $r$, this paper also presents a general method for constructing a lager normal mixed difference matrix of order $r(r+1)$. Furthermore, if the difference matrix of order $r$ does not exist but an orthogonal array of runs $r^2$ exists, we can also construct a lager normal mixed difference matrix from the normal mixed difference matrix of order $r+1$ and the orthogonal array of runs $r^2$.