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Following are three statements. In a Markov chain, a persistent state i is a null persistent if :

(I) \(\limsup p_{ii}^{(n)} = 0\)
(II) mean recurrence time is \(\infty\)
(III) \(\limsup p_{ii}^{(n)} \gt 0\)

Which of the following is true ?

  • A.Only (I) is true
  • B.Both (I) and (II) are true
  • C.Only (III) is true
  • D.Both (II) and (III) are true

Answer: B

Both (I) and (II) are true.

A persistent (recurrent) state is null persistent when its mean recurrence time \(\mu_{i}\) is infinite; that is the definition, so (II) is true. For such a state \(p_{ii}^{(n)} \to 0\), so \(\limsup p_{ii}^{(n)} = 0\) and (I) is true.

A positive persistent state has finite mean recurrence time and, if aperiodic, \(p_{ii}^{(n)} \to 1/\mu_{i} \gt 0\). So \(\limsup p_{ii}^{(n)} \gt 0\) characterises positive persistence, and (III) is false for a null persistent state.

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