/**
* Update this model using the differences between the correct output and the predicted output,
* both given as arguments.
*
* @param input
* @param outputCorrect
* @param outputPredicted
* @param learningRate
* @return
*/
private double update(
DPInput input, DPOutput outputCorrect, DPOutput outputPredicted, double learningRate) {
/*
* The root token (zero) must always be ignored during the inference and
* so its always correctly classified (its head must always be pointing
* to itself).
*/
assert outputCorrect.getHead(0) == outputPredicted.getHead(0);
// Per-token loss value for this example.
double loss = 0d;
for (int idxTkn = 1; idxTkn < input.getNumberOfTokens(); ++idxTkn) {
int idxCorrectHead = outputCorrect.getHead(idxTkn);
int idxPredictedHead = outputPredicted.getHead(idxTkn);
if (idxCorrectHead == idxPredictedHead)
// Correctly predicted head.
continue;
if (idxCorrectHead == -1)
/*
* Skip tokens with missing CORRECT edge (this is due to prune
* preprocessing).
*/
continue;
// Misclassified head. Increment missed edges weights.
int[] correctFeatures = input.getFeatures(idxCorrectHead, idxTkn);
for (int idxFtr = 0; idxFtr < correctFeatures.length; ++idxFtr) {
int ftr = correctFeatures[idxFtr];
AveragedParameter param = getFeatureWeightOrCreate(ftr);
param.update(learningRate);
updatedWeights.add(param);
}
if (idxPredictedHead == -1) {
LOG.warn("Predicted head is -1");
continue;
}
// Decrement mispredicted edges weights.
int[] predictedFeatures = input.getFeatures(idxPredictedHead, idxTkn);
for (int idxFtr = 0; idxFtr < predictedFeatures.length; ++idxFtr) {
int ftr = predictedFeatures[idxFtr];
AveragedParameter param = getFeatureWeightOrCreate(ftr);
param.update(-learningRate);
updatedWeights.add(param);
}
// Increment (per-token) loss value.
loss += 1d;
}
return loss;
}
@Override
public double getEdgeScore(DPInput input, int idxHead, int idxDependent) {
double score = 0d;
// Accumulate the parameter in the edge score.
int[] ftrs = input.getFeatures(idxHead, idxDependent);
if (ftrs == null)
// Edge does not exist.
return Double.NaN;
for (int ftr : ftrs) {
AveragedParameter param = getFeatureWeight(ftr);
if (param != null) score += param.get();
}
return score;
}