The concept of the rank of a -matrices is the same as that of a constant matrix. Thus, the highest order of the minors of not being identically zero is called the rank of a -matrices. It is to be noted that minors of are polynomials in. By a polynomial in being identically zero we mean that any number can be its root. Hence its coefficients are all zero, and we often say that the polynomial is identically equal to zero. Because any polynomial of degree only can have roots, it is not a null polynomial, i.e., not a polynomial vanishing identically.