Class PolynomialTransform

JSAT/src/jsat/datatransform/PolynomialTransform.java:17–139

A transform for applying a polynomial transformation on the data set. As the dimension of the data set grows, the number of new features created by a polynomial transform grows rapidly. It is recommended only for small dimension problems using small degrees. @author Edward Raff

 * @author Edward Raff
 */
public class PolynomialTransform implements DataTransform
{

    private static final long serialVersionUID = -5332216444253168283L;
    private int degree;

    /**
     * Creates a new polynomial transform of the given degree
     * @param degree the degree of the polynomial
     * @throws ArithmeticException if the degree is not greater than 1
     */
    public PolynomialTransform(int degree)
    {
        if(degree < 2)
            throw new ArithmeticException("The degree of the polynomial was a nonsense value: " + degree);
        this.degree = degree;
    }

    @Override
    public void fit(DataSet data)
    {
        //no-op, nothing needs to be done
    }
    
    @Override
    public DataPoint transform(DataPoint dp)
    {
        Vec x = dp.getNumericalValues();
        int[] setTo = new int[x.length()];
        
        //TODO compute final size directly isntead of doing a pre loop
        int finalSize = 0;
        
        int curCount = increment(setTo, degree, 0);
        do
        {
            finalSize++;
            curCount = increment(setTo, degree, curCount);
        }
        while(setTo[x.length()-1] <= degree);
        
        
        
        
        double[] newVec = new double[finalSize];
        Arrays.fill(newVec, 1.0);
        int index = 0;
        
        Arrays.fill(setTo, 0);
        curCount = increment(setTo, degree, 0);
        do
        {
            for(int i = 0; i < setTo.length; i++)
                if(setTo[i] > 0)
                    newVec[index] *= Math.pow(x.get(i), setTo[i]);
            index++;
            curCount = increment(setTo, degree, curCount);
        }