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7. Hidden Markov Models (Parte 2) (pdf, it, 413 KB, 4/28/10)

7. Hidden Markov Models (Parte 2) (pdf, it, 413 KB, 4/28/10)

7. Hidden Markov Models (Parte 2) (pdf, it, 413 KB, 4/28/10)

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Model selection: solutions<br />

• Typical solution (usable for many probabilistic<br />

models)<br />

– train several models w<strong>it</strong>h different orders k<br />

– choose the one maximizing an “optimal<strong>it</strong>y” cr<strong>it</strong>erion<br />

Which “optimal<strong>it</strong>y” cr<strong>it</strong>erion?<br />

• First naive solution: maximizing likelihood of<br />

data w.r.t. model<br />

Maximizing Log Likelihood<br />

• Problem: Log Likelihood is not decreasing<br />

when augmenting the order<br />

-50<br />

-<strong>10</strong>0<br />

-150<br />

-200<br />

-250<br />

0 5 <strong>10</strong> 15 20<br />

Not applicable cr<strong>it</strong>erion!<br />

54<br />

55<br />

4

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