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SOLUTIONS MANUAL for Stochastic Modeling: Analysis and ...

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90 CHAPTER 7. CONTINUOUS-TIME PROCESSES<br />

19.<br />

an exponential distribution.<br />

This result shows that we can represent the holding time in a state (which is exponentially<br />

distributed) as the sum of a geometrically distributed number of exponentially<br />

distributed r<strong>and</strong>om variables with a common rate. This is precisely what uni<strong>for</strong>mization<br />

does.<br />

p ij (t) = e −g∗ t<br />

∞∑<br />

n=0<br />

q (n)<br />

ij<br />

= ˜p ij (t)+e −g∗ t<br />

≥<br />

˜p ij (t)<br />

because g ∗ > 0, t>0<strong>and</strong>q (n)<br />

ij ≥ 0.<br />

Notice that<br />

(g ∗ t) n<br />

n!<br />

∞∑<br />

n=n ∗ +1<br />

q (n)<br />

ij<br />

(g ∗ t) n<br />

n!<br />

e −g∗ t<br />

∞∑<br />

n=n ∗ +1<br />

q (n)<br />

ij<br />

(g ∗ t) n<br />

n!<br />

= 1− e −g∗ t<br />

≤<br />

1 − e −g∗ t<br />

n∗ ∑<br />

n=0<br />

n∗ ∑<br />

n=0<br />

q (n)<br />

ij<br />

(g ∗ t) n<br />

n!<br />

(g ∗ t) n<br />

n!<br />

because q (n)<br />

ij ≤ 1.<br />

20.<br />

Pr{Z 1 ≤ min<br />

j≠1<br />

Z j,H >t}<br />

= Pr{Z 1 ≤ Z 2 ,...,Z 1 ≤ Z k ,Z 1 >t,...,Z k >t}<br />

= Pr{t

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