0 ). 0 Y 7 4. Any two square matrices Xmxm and Ynxn can be "diagonally concatenated to form a X (m + n) x (m + n) matrix as in X BY := called the diagonal sum (or more precisely, diagonal direct sum) of X and Y , where each 0 represents a zero matrix of appro- priate size. (i) Describe the size of each 0 in the above X&Y. (ii) Describe the entries Crs of Ik H0e =: (Crs)rs (with ranges of r and s explicitly specified) in terms of O and the Kronecker delta symbol. (iii) For what size of a matrix A = (aij)ij is the product A (Ik. 80e) meaningful, and how is A (Ik 80e) related to A? Specify the ranges of p and q, and give p explicit formula of each bp, in terms of the entries of A. Then describe/summarize verbally how A is altered by the multiplication A (Ik # 0e) of A by Ik # 0e on the right. =: = =! (bpa) pa