maxenttrainer.java

mallet是自然语言处理、机器学习领域的一个开源项目。

			this.trainingList = ilist;
			Alphabet fd = ilist.getDataAlphabet();
			LabelAlphabet ld = (LabelAlphabet) ilist.getTargetAlphabet();
			// Don't fd.stopGrowth, because someone might want to do feature induction
			ld.stopGrowth();
			// Add one feature for the "default feature".
			this.numLabels = ld.size();
			this.numFeatures = fd.size() + 1;
			this.defaultFeatureIndex = numFeatures-1;
			this.parameters = new double [numLabels * numFeatures];
			this.constraints = new double [numLabels * numFeatures];
			this.cachedGradient = new double [numLabels * numFeatures];
			Arrays.fill (parameters, 0.0);
			Arrays.fill (constraints, 0.0);
			Arrays.fill (cachedGradient, 0.0);
			this.featureSelection = ilist.getFeatureSelection();
			this.perLabelFeatureSelection = ilist.getPerLabelFeatureSelection();
			// Add the default feature index to the selection
			if (featureSelection != null)
				featureSelection.add (defaultFeatureIndex);
			if (perLabelFeatureSelection != null)
				for (int i = 0; i < perLabelFeatureSelection.length; i++)
					perLabelFeatureSelection[i].add (defaultFeatureIndex);
			// xxx Later change this to allow both to be set, but select which one to use by a boolean flag?
			assert (featureSelection == null || perLabelFeatureSelection == null);
			if (initialClassifier != null) {

        this.theClassifier = initialClassifier;
        this.parameters = theClassifier.parameters;
        this.featureSelection = theClassifier.featureSelection;
        this.perLabelFeatureSelection = theClassifier.perClassFeatureSelection;
        this.defaultFeatureIndex = theClassifier.defaultFeatureIndex;
				assert (initialClassifier.getInstancePipe() == ilist.getPipe());
			}
			else if (this.theClassifier == null) {
				this.theClassifier = new MaxEnt (ilist.getPipe(), parameters, featureSelection, perLabelFeatureSelection);
			}
			cachedValueStale = true;
			cachedGradientStale = true;

			// Initialize the constraints
			InstanceList.Iterator iter = trainingList.iterator ();
			logger.fine("Number of instances in training list = " + trainingList.size());
			while (iter.hasNext()) {
				double instanceWeight = iter.getInstanceWeight();
				Instance inst = iter.nextInstance();
				Labeling labeling = inst.getLabeling ();
				//logger.fine ("Instance "+ii+" labeling="+labeling);
				FeatureVector fv = (FeatureVector) inst.getData ();
				Alphabet fdict = fv.getAlphabet();
				assert (fv.getAlphabet() == fd);
				int li = labeling.getBestIndex();
				MatrixOps.rowPlusEquals (constraints, numFeatures, li, fv, instanceWeight);
				// For the default feature, whose weight is 1.0
				assert(!Double.isNaN(instanceWeight)) : "instanceWeight is NaN";
				assert(!Double.isNaN(li)) : "bestIndex is NaN";
				boolean hasNaN = false;
				for(int i = 0; i < fv.numLocations(); i++) {
					if(Double.isNaN(fv.valueAtLocation(i))) {
						logger.info("NaN for feature " + fdict.lookupObject(fv.indexAtLocation(i)).toString());
						hasNaN = true;
					}
				}
				if(hasNaN)
					logger.info("NaN in instance: " + inst.getName());

				constraints[li*numFeatures + defaultFeatureIndex] += 1.0 * instanceWeight;
			}
			//TestMaximizable.testValueAndGradientCurrentParameters (this);
		}

		public MaxEnt getClassifier () { return theClassifier; }

		public double getParameter (int index) {
			return parameters[index];
		}

		public void setParameter (int index, double v) {
			cachedValueStale = true;
			cachedGradientStale = true;
			parameters[index] = v;
		}

		public int getNumParameters() {
			return parameters.length;
		}

		public void getParameters (double[] buff) {
			if (buff == null || buff.length != parameters.length)
				buff = new double [parameters.length];
			System.arraycopy (parameters, 0, buff, 0, parameters.length);
		}

		public void setParameters (double [] buff) {
			assert (buff != null);
			cachedValueStale = true;
			cachedGradientStale = true;
			if (buff.length != parameters.length)
				parameters = new double[buff.length];
			System.arraycopy (buff, 0, parameters, 0, buff.length);
		}


		// log probability of the training labels
		public double getValue ()
		{
			if (cachedValueStale) {
				numGetValueCalls++;
				cachedValue = 0;
				// We'll store the expectation values in "cachedGradient" for now
				cachedGradientStale = true;
				MatrixOps.setAll (cachedGradient, 0.0);
				// Incorporate likelihood of data
				double[] scores = new double[trainingList.getTargetAlphabet().size()];
				double value = 0.0;
                //System.out.println("I Now "+inputAlphabet.size()+" regular features.");
				InstanceList.Iterator iter = trainingList.iterator();
				int ii=0;
				while (iter.hasNext()) {
					ii++;
					double instanceWeight = iter.getInstanceWeight();
					Instance instance = iter.nextInstance();
					Labeling labeling = instance.getLabeling ();
                    //System.out.println("L Now "+inputAlphabet.size()+" regular features.");

					this.theClassifier.getClassificationScores (instance, scores);
					FeatureVector fv = (FeatureVector) instance.getData ();
					int li = labeling.getBestIndex();
					value = - (instanceWeight * Math.log (scores[li]));
					if(Double.isNaN(value)) {
						logger.fine ("MaxEntTrainer: Instance " + instance.getName() +
												 "has NaN value. log(scores)= " + Math.log(scores[li]) +
												 " scores = " + scores[li] +
												 " has instance weight = " + instanceWeight);

					}
					if (Double.isInfinite(value)) {
						logger.warning ("Instance "+instance.getSource() + " has infinite value; skipping value and gradient");
						cachedValue -= value;
						cachedValueStale = false;
						return -value;
//						continue;
					}
					cachedValue += value;
                    // CPAL - this is a loop over classes and their scores
                    //      - we compute the gradient by taking the dot product of the feature value
                    //        and the probability of the class
                    for (int si = 0; si < scores.length; si++) {
						if (scores[si] == 0) continue;
						assert (!Double.isInfinite(scores[si]));
                        // CPAL - accumulating the current classifiers expectation of the feature
                        // vector counts for this class label
                        // Current classifier has expectation over class label, not over feature vector
                        MatrixOps.rowPlusEquals (cachedGradient, numFeatures,
						si, fv, -instanceWeight * scores[si]);
						cachedGradient[numFeatures*si + defaultFeatureIndex] += (-instanceWeight * scores[si]);
					}

                    // CPAL - if we wish to do multiconditional training we need another term for this accumulated
                    //        expectation
                    if (usingMultiConditionalTraining) {
                        // need something analogous to this
                        // this.theClassifier.getClassificationScores (instance, scores);
                        // this.theClassifier.getFeatureDistributions (instance,
                        // Note: li is the "label" for this instance

                        for (int fi = 0; fi < numFeatures; fi++) {

                            //if(parameters[numFeatures*li + fi] != 0) {
                            // MatrixOps.rowPlusEquals(cachedGradient, numFeatures,li,fv,))
                                cachedGradient[numFeatures*li + fi] += (-instanceWeight * Math.exp(parameters[numFeatures*li + fi]));
                            //    }
                        }

                    }
                }
					//logger.info ("-Expectations:"); cachedGradient.print();
				// Incorporate prior on parameters
				if (usingHyperbolicPrior) {
					for (int li = 0; li < numLabels; li++)
						for (int fi = 0; fi < numFeatures; fi++)
							cachedValue += (hyperbolicPriorSlope / hyperbolicPriorSharpness
														 * Math.log (Maths.cosh (hyperbolicPriorSharpness * parameters[li *numFeatures + fi])));
				} else {
					for (int li = 0; li < numLabels; li++)
						for (int fi = 0; fi < numFeatures; fi++) {
							double param = parameters[li*numFeatures + fi];
							cachedValue += param * param / (2 * gaussianPriorVariance);
						}
				}
				cachedValue *= -1.0; // MAXIMIZE, NOT MINIMIZE
				cachedValueStale = false;
				progressLogger.info ("Value (loglikelihood) = "+cachedValue);
			}
			return cachedValue;
		}

 // CPAL first get value, then gradient

        public void getValueGradient (double [] buffer)
		{
			// Gradient is (constraint - expectation - parameters/gaussianPriorVariance)
			if (cachedGradientStale) {
				numGetValueGradientCalls++;
				if (cachedValueStale)
					// This will fill in the cachedGradient with the "-expectation"
					getValue ();
                // cachedGradient contains the negative expectations
                // expectations are model expectations and constraints are
                // empirical expectations
                MatrixOps.plusEquals (cachedGradient, constraints);
                // CPAL - we need a second copy of the constraints
                if (usingMultiConditionalTraining){
                    MatrixOps.plusEquals(cachedGradient, constraints);
                }
                // Incorporate prior on parameters
				if (usingHyperbolicPrior) {
					throw new UnsupportedOperationException ("Hyperbolic prior not yet implemented.");
				}
				else {
					MatrixOps.plusEquals (cachedGradient, parameters,
																-1.0 / gaussianPriorVariance);
				}

				// A parameter may be set to -infinity by an external user.
				// We set gradient to 0 because the parameter's value can
				// never change anyway and it will mess up future calculations
				// on the matrix, such as norm().
				MatrixOps.substitute (cachedGradient, Double.NEGATIVE_INFINITY, 0.0);
				// Set to zero all the gradient dimensions that are not among the selected features
				if (perLabelFeatureSelection == null) {
					for (int labelIndex = 0; labelIndex < numLabels; labelIndex++)
						MatrixOps.rowSetAll (cachedGradient, numFeatures,
																 labelIndex, 0.0, featureSelection, false);
				} else {
					for (int labelIndex = 0; labelIndex < numLabels; labelIndex++)
						MatrixOps.rowSetAll (cachedGradient, numFeatures,
																 labelIndex, 0.0,
																 perLabelFeatureSelection[labelIndex], false);
				}
				cachedGradientStale = false;
			}
			assert (buffer != null && buffer.length == parameters.length);
			System.arraycopy (cachedGradient, 0, buffer, 0, cachedGradient.length);
		}
	}

}