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Linear Algebra, Theory And Applications, 2012a

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11.3. MARKOV CHAINS 281<br />

After many iterations of the process, if you start at 2 you will end up at 1 with probability<br />

2/3 and at 4 with probability 1/3. This makes good intuitive sense because it is twice as far<br />

from 2 to 4 as it is from 2 to 1.<br />

Theorem 11.3.4 The eigenvalues of<br />

⎛<br />

⎞<br />

0 p 0 ··· 0<br />

q 0 p ··· 0<br />

. 0 q 0 ..<br />

. ⎜<br />

.<br />

⎝ . 0 .. . .. p ⎟<br />

⎠<br />

0 . 0 q 0<br />

have absolute value less than 1. Here p + q =1and both p, q > 0.<br />

Proof: By Gerschgorin’s theorem, if λ is an eigenvalue, then |λ| ≤1. Now suppose v<br />

is an eigenvector for λ. Then<br />

⎛<br />

⎞ ⎛ ⎞<br />

pv 2<br />

v 1<br />

qv 1 + pv 3<br />

v 2<br />

Av =<br />

⎜ .<br />

= λ<br />

⎟ ⎜ .<br />

⎟<br />

⎝ qv n−2 + pv n<br />

⎠ ⎝ v n−1<br />

⎠<br />

qv n−1<br />

v n<br />

Suppose |λ| =1. Then the top row shows p |v 2 | = |v 1 | so |v 1 | < |v 2 | . Suppose |v 1 | < |v 2 | <<br />

···< |v k | for some k

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