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Consider a Markov chain on \(S = \{1, 2, 3, 4, 5\}\) with its transition probability matrix given by :

P12345
13/401/400
21/2001/20
31/201/200
40002/31/3
50001/32/3

Then :

  • A.there exists a unique stationary distribution
  • B.there does not exist any stationary distribution
  • C.all states are transient
  • D.there exist infinitely many stationary distributions

Answer: D

There exist infinitely many stationary distributions.

From states 1 and 3 the chain moves only between 1 and 3, so {1, 3} is a closed recurrent class. Likewise {4, 5} is closed and recurrent. State 2 leads to 1 or 4 and never returns, so it is transient.

Each closed class has its own stationary distribution: on {1, 3}, \(\pi_{1} = 2/3, \pi_{3} = 1/3\); on {4, 5}, \(\pi_{4} = \pi_{5} = 1/2\). Every convex combination of the two is also stationary, giving infinitely many.

Uniqueness (A) needs a single recurrent class. Not all states are transient (C), and with a finite chain at least one stationary distribution always exists (B fails).

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