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The observation sequences <strong>of</strong> three variables are denoted by Y 1<br />

, Y 2<br />

, Y 3<br />

row vectors<br />

(with uppercase letters)<br />

Y<br />

1<br />

= ⎡ ⎣ y11 y12 ... y1j<br />

... y ⎤<br />

1n<br />

⎦ .<br />

Y<br />

2<br />

= ⎡ ⎣ y21 y22 ... y2 j<br />

... y ⎤<br />

2n<br />

⎦ .<br />

Y<br />

3<br />

= ⎡ ⎣ y31 y32 ... y3j<br />

... y ⎤<br />

3n<br />

⎦ .<br />

To denote the observation sets we will use column vectors<br />

y ,...,<br />

1<br />

, y<br />

2<br />

y<br />

n<br />

(with lowercase<br />

letters)<br />

y<br />

1<br />

⎡ y<br />

=<br />

⎢<br />

⎢<br />

y<br />

⎢⎣<br />

y<br />

11<br />

21<br />

31<br />

⎤<br />

⎥<br />

⎥<br />

⎥⎦<br />

⎡ y12<br />

⎤<br />

y<br />

⎢ ⎥<br />

2<br />

=<br />

⎢<br />

y22<br />

⎥<br />

…<br />

⎢⎣<br />

y ⎥<br />

32 ⎦<br />

⎡ y1<br />

n ⎤<br />

y<br />

⎢ ⎥<br />

n<br />

=<br />

⎢<br />

y2n<br />

⎥<br />

.<br />

⎢⎣<br />

y ⎥<br />

3n<br />

⎦<br />

Then Y = ⎡ ⎣ y1 y2 ... y<br />

j<br />

... y ⎤<br />

n ⎦ where y<br />

n<br />

is a trivariate observation.<br />

5.4.2 Estimation <strong>for</strong> the <strong>multivariate</strong> Poisson <strong>hidden</strong> Markov <strong>models</strong> (Extension <strong>of</strong><br />

the univariate Markov-dependent mixture model by Leroux and Puterman, 1992)<br />

Let Y= ⎡ ⎣ y1 y2 . . . yj<br />

. . . y ⎤<br />

n ⎦ be the realization <strong>of</strong> a <strong>hidden</strong> Markov model<br />

with original m state Markov Chain { i<br />

}<br />

S . Define Φ by ( P P ,..., , λ , λ ,..., λ )<br />

11<br />

,<br />

12<br />

P mm 1 2<br />

m<br />

92

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