How to find the sum of all entries in the matrix $A^5$

Question

Let $A$ be a $4 × 4$ matrix with non-negative entries such that the sum of the entries in each row of $A$ equals $1$. Find the sum of all entries in the matrix $A^5$.

If $A=I_4$ then $A^5=I_4$ and sum of all entries in the matrix $A^5=4$. But how I show the general result. Please help.

score 13 · Accepted Answer · answered Jan 27 '13 at 13:32

13

Let $j=\left(\begin{matrix}1\\\vdots\\1\end{matrix}\right)$. Then the sum of entries of matrix $A^5$ is just $j^TA^5j$. What can you say about $Aj$?

answered Jan 27 '13 at 13:32

Hagen von Eitzen

374,180

1

I think $Aj=j$. Am I correct? – A.D Jan 27 '13 at 13:55
@A.D Yes, because $(1,j)$ is an eigenpair of $A$. – Git Gud Jan 27 '13 at 13:57
I am sorry...I cant get the concept..will you please explain little more briefly..how will you multiply $A^5$ and $j$. – Sam Christopher May 23 '16 at 06:14
@SamChristopher Use the relation : If $( \lambda, v )$ is Eigen pair for $A$ then $ A^n v = \lambda^n v $ for all $v$ – Ravindra Jun 08 '20 at 18:00

How to find the sum of all entries in the matrix $A^5$

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