The sum of row elements is 3, which means that the sum of each row is 3, and the corresponding A left multiplication (1, 1, 1)T equals (3,3,3) t to get the expression in the analysis, and 3 can be an eigenvalue (I think you don't know why the left multiplication is generated, but you still don't understand the significance of matrix multiplication). In addition, the title notification rank is 1, so there is only one non-zero eigenvalue, which is 3, so the other two are 0.