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@ -21,39 +21,39 @@ namespace paddle {
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class LinearChainCRF {
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public:
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/*
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The size of para and grad must be (numClasses + 2) * numClasses.
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The first numClasses values of para are for starting weights (a).
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The next numClasses values of para are for ending weights (b),
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The remaning values are for transition weights (w).
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The probability of a state sequence s of length L is defined as:
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P(s) = (1/Z) exp(a_{s_1} + b_{s_L}
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+ \sum_{l=1}^L x_{s_l}
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+ \sum_{l=2}^L w_{s_{l-1},s_l})
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where Z is a normalization value so that the sum of P(s) over all possible
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sequences is 1, and x is the input feature to the CRF.
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/**
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* The size of para and grad must be \f$(numClasses + 2) * numClasses\f$.
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* The first numClasses values of para are for starting weights (\f$a\f$).
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* The next numClasses values of para are for ending weights (\f$b\f$),
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* The remaning values are for transition weights (\f$w\f$).
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*
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* The probability of a state sequence s of length \f$L\f$ is defined as:
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* \f$P(s) = (1/Z) exp(a_{s_1} + b_{s_L}
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* + \sum_{l=1}^L x_{s_l}
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* + \sum_{l=2}^L w_{s_{l-1},s_l})\f$
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* where \f$Z\f$ is a normalization value so that the sum of \f$P(s)\f$ over all possible
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* sequences is \f$1\f$, and \f$x\f$ is the input feature to the CRF.
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*/
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LinearChainCRF(int numClasses, real* para, real* grad);
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/*
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Calculate the negative log likelihood of s given x.
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The size of x must be length * numClasses. Each consecutive numClasses
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values are the features for one time step.
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/**
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* Calculate the negative log likelihood of s given x.
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* The size of x must be length * numClasses. Each consecutive numClasses
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* values are the features for one time step.
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*/
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real forward(real* x, int* s, int length);
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/*
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Calculate the gradient with respect to x, a, b, and w.
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The gradient of x will be stored in dx.
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backward() can only be called after a corresponding call to forward() with
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the same x, s and length.
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NOTE: The gradient is added to dx and grad (provided at constructor).
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/**
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* Calculate the gradient with respect to x, a, b, and w.
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* The gradient of x will be stored in dx.
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* backward() can only be called after a corresponding call to forward() with
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* the same x, s and length.
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* @note The gradient is added to dx and grad (provided at constructor).
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*/
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void backward(real* x, real* dx, int* s, int length);
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/*
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Find the most probable sequence given x. The result will be stored in s.
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/**
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* Find the most probable sequence given x. The result will be stored in s.
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*/
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void decode(real* x, int* s, int length);
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