Changeset 1182 for trunk/yat/classifier
 Timestamp:
 Feb 28, 2008, 1:27:37 PM (13 years ago)
 Location:
 trunk/yat/classifier
 Files:

 2 edited
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trunk/yat/classifier/NBC.cc
r1162 r1182 152 152 prediction.resize(centroids_.columns(), mlw.columns(), 0); 153 153 154 // first calculate lnP = sum sigma_i + (x_im_i)^2/2sigma_i^2 154 // first calculate lnP = sum (sigma_i) + 155 // N sum w_i(x_im_i)^2/2sigma_i^2 / sum w_i 155 156 for (size_t label=0; label<centroids_.columns(); ++label) { 156 157 double sum_log_sigma = sum_logsigma(label); 157 158 for (size_t sample=0; sample<prediction.rows(); ++sample) { 158 prediction(label,sample) = sum_log_sigma;159 statistics::AveragerWeighted aw; 159 160 for (size_t i=0; i<mlw.rows(); ++i) 160 // taking care of NaN and missing training features 161 if (mlw.weight(i, label) && !std::isnan(sigma2_(i, label))) { 162 prediction(label, sample) += mlw.weight(i, label)* 163 std::pow(mlw.data(i, label)centroids_(i, label),2)/ 164 sigma2_(i, label); 165 } 166 161 // missing training features 162 if (!std::isnan(sigma2_(i, label))) 163 aw.add(std::pow(mlw.data(i, label)centroids_(i, label),2)/ 164 sigma2_(i, label), mlw.weight(i, label)); 165 prediction(label,sample) = sum_log_sigma + mlw.rows()*aw.mean()/2; 167 166 } 168 167 } 
trunk/yat/classifier/NBC.h
r1169 r1182 104 104 row in \a res corresponds to a class. The prediction is the 105 105 estimated probability that sample belong to class \f$ j \f$ 106 107 \f$ P_j = \frac{1}{Z}\prod_i\({\frac{1}{\sqrt{2\pi\sigma_i^2}}}\) 108 \exp(\frac{\sum{w_i(x_i\mu_i)^2}{\sigma_i^2}}{\sum w_i})\f$, 109 where \f$ \mu_i 110 \f$ and \f$ \sigma_i^2 \f$ are the estimated mean and variance, 111 respectively. If a \f$ \sigma_i \f$ could not be estimated 112 during training, corresponding factor is set to unity, in other 113 words, that feature is ignored for the prediction of that 114 particular class. Z is chosen such that total probability, \f$ 115 \sum P_j \f$, equals unity. 106 116 */ 107 117 void predict(const MatrixLookupWeighted& data, utility::Matrix& res) const;
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