# Markov chain transition matrix with each row the same?

In my linear algebra class, we were learning about Markov chains, and the prof. put a confusing question on the board. Namely, can one have a transition matrix in which each row is the same, i.e., let's say for a $3 \times 3$ matrix, each row is $[a,b,c]$, with the constraint being that $a + b +c =1$. Is this possible? Further, what if the values of $a,b,c$ are the same as the values of the steady-state vector?

• Why not? It might be a peculiar Markov chain, but the matrix fits all the conditions. – kimchi lover Aug 10 '17 at 2:47

The values $a,b,c$ are going to be the values of the steady state vector - we can think about this as such: in the long run, the probability from going from any state to state 1 is $a$, and correspondingly $b$ and $c$ for states 2 and 3 respectively.
A Markov chain $X_1, X_2, \dots$ with a transition matrix in which each row is the same corresponds to the special case in which each $X_i$ is independent of $X_{i-1}.$
In general, a Markov chain has $$P(X_i = x_i|X_{i-1}=x_{i-1},\, X_{i-2} = x_{i-2},\, \dots,\, X_{i-k} = x_{i-l}) = P(X_i = x_i|X_{i-1}=x_{i-1}),$$ so colloquially, dependence is only on the most recent specified step. However, there is no requirement for any dependence at all. An sequence of independent random variables can be Markovian.
Note: The power $P^n$ of a Markov chain shows $n$-step transition probabilities. Some Markov chains have the property that $P^n,$ for sufficiently large $n,$ has rows that are very nearly the same, indicating that $\lim_{n\rightarrow\infty} P^n$ exists. This means that, with sufficient passage of time, the state of a Markov chain at step $n$ does not depend on its initial state at step $1.$ A chain with such limiting distribution is called ergodic.