DEFINTION3 Matrices 矩阵 Leta=ai and b=bi be m X n matrices. The sum of A and b, denoted by a+ B, is the m x n matrix that has ai t bi as its (i,j)th element. In other words,A+ b ai +bilM a t r i c e s 矩 阵 DEFINITION 3. Let A = [aij] and B = [bij] be m × n matrices. The sum of A and B, denoted by A + B, is the m × n matrix that has aij + bij as its (i, j)th element. In other words, A + B = [aij +bij]