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courses:rg:2013:crf [2013/03/29 07:50]
ufal vytvořeno 		courses:rg:2013:crf [2013/03/29 09:00] (current)
popel typos fixed
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 (2) MEMMs suffer from Label Bias Problem. What about HMMs? Why? (2) MEMMs suffer from Label Bias Problem. What about HMMs? Why?
  
-(3) Which of the following features are meaningfull? Why?+(3) Which of the following features are meaningful? Why?
  
 a) <latex>X_i</latex> == can a) <latex>X_i</latex> == can
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 g) <latex>X_{i+3}</latex> == can && <latex>Y_i</latex> == N && <latex>Y_{i-2}</latex> == V g) <latex>X_{i+3}</latex> == can && <latex>Y_i</latex> == N && <latex>Y_{i-2}</latex> == V
 h) <latex>X_1</latex> == The && <latex>Y_{i-1}</latex> == N && <latex>Y_i</latex> == N h) <latex>X_1</latex> == The && <latex>Y_{i-1}</latex> == N && <latex>Y_i</latex> == N
-i) <latex>X_i</latex> has more letters than <latex>X_{i-1}</latex> && Y_i</latex> == N +i) <latex>X_i</latex> has more letters than <latex>X_{i-1}</latex> && <latex>Y_i</latex> == N 
-j) <latex>X</latex> contains word "dog" && (<latex>Y_i</latex> == N || <latex>Y_i</latex> == V)+j) <latex> X</latex> contains word "dog" && (<latex>Y_i</latex> == N || <latex>Y_i</latex> == V)
  
 (4) Let's suppose, that we have a CRF for the data "he/N can/V can/V a/N can/N" and these features: (4) Let's suppose, that we have a CRF for the data "he/N can/V can/V a/N can/N" and these features:
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 <latex>g_1</latex>: <latex>X_i</latex> == he && <latex>Y_i</latex> = N <latex>g_1</latex>: <latex>X_i</latex> == he && <latex>Y_i</latex> = N
  
-a) |Y| = ?+a) |<latex>\cal{Y}</latex>| = ?
 b) Draw a CRF for given data! b) Draw a CRF for given data!
-c) Simplify (as much as possible) the exp(...) expression in Formula 1, gived the above definitions of <latex>f_1</latex>, <latex>f_2</latex> and <latex>g_1</latex>.+c) Simplify (as much as possible) the exp(...) expression in Formula 1, given the above definitions of <latex>f_1</latex>, <latex>f_2</latex> and <latex>g_1</latex>.
  
 **Hint1:** The alpha-like symbol means "is directly proportional", i.e. <latex>A \propto B \Leftrightarrow A = k * B</latex> && <latex>k \neq 0</latex> **Hint1:** The alpha-like symbol means "is directly proportional", i.e. <latex>A \propto B \Leftrightarrow A = k * B</latex> && <latex>k \neq 0</latex>

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