/**
* Outputs the distribution for the given output.
*
* <p>Pipes output of SVM through sigmoid function.
*
* @param inst the instance for which distribution is to be computed
* @return the distribution
* @exception Exception if something goes wrong
*/
public double[] distributionForInstance(Instance inst) throws Exception {
// Filter instance
m_ReplaceMissingValues.input(inst);
m_ReplaceMissingValues.batchFinished();
inst = m_ReplaceMissingValues.output();
m_NominalToBinary.input(inst);
m_NominalToBinary.batchFinished();
inst = m_NominalToBinary.output();
// Get probabilities
double output = 0, sumSoFar = 0;
if (m_K > 0) {
for (int i = 0; i <= m_K; i++) {
if (sumSoFar < 0) {
output -= m_Weights[i];
} else {
output += m_Weights[i];
}
if (m_IsAddition[i]) {
sumSoFar += innerProduct(m_Train.instance(m_Additions[i]), inst);
} else {
sumSoFar -= innerProduct(m_Train.instance(m_Additions[i]), inst);
}
}
}
double[] result = new double[2];
result[1] = 1 / (1 + Math.exp(-output));
result[0] = 1 - result[1];
return result;
}
/**
* Builds the ensemble of perceptrons.
*
* @exception Exception if something goes wrong during building
*/
public void buildClassifier(Instances insts) throws Exception {
if (insts.checkForStringAttributes()) {
throw new UnsupportedAttributeTypeException("Cannot handle string attributes!");
}
if (insts.numClasses() > 2) {
throw new Exception("Can only handle two-class datasets!");
}
if (insts.classAttribute().isNumeric()) {
throw new UnsupportedClassTypeException("Can't handle a numeric class!");
}
// Filter data
m_Train = new Instances(insts);
m_Train.deleteWithMissingClass();
m_ReplaceMissingValues = new ReplaceMissingValues();
m_ReplaceMissingValues.setInputFormat(m_Train);
m_Train = Filter.useFilter(m_Train, m_ReplaceMissingValues);
m_NominalToBinary = new NominalToBinary();
m_NominalToBinary.setInputFormat(m_Train);
m_Train = Filter.useFilter(m_Train, m_NominalToBinary);
/** Randomize training data */
m_Train.randomize(new Random(m_Seed));
/** Make space to store perceptrons */
m_Additions = new int[m_MaxK + 1];
m_IsAddition = new boolean[m_MaxK + 1];
m_Weights = new int[m_MaxK + 1];
/** Compute perceptrons */
m_K = 0;
out:
for (int it = 0; it < m_NumIterations; it++) {
for (int i = 0; i < m_Train.numInstances(); i++) {
Instance inst = m_Train.instance(i);
if (!inst.classIsMissing()) {
int prediction = makePrediction(m_K, inst);
int classValue = (int) inst.classValue();
if (prediction == classValue) {
m_Weights[m_K]++;
} else {
m_IsAddition[m_K] = (classValue == 1);
m_Additions[m_K] = i;
m_K++;
m_Weights[m_K]++;
}
if (m_K == m_MaxK) {
break out;
}
}
}
}
}