Method weightedDot

JSAT/src/jsat/linear/VecOps.java:102–148

Computes the weighted dot product of ∑ ∀ i ∈ |w| w_i x_i y_i @param w the vector containing the weights, it is assumed to be random access @param x the first vector of the dot product @param y the second vector of the dot product @return the weighted dot product,

(final Vec w, final Vec x, final Vec y)

     * @return the weighted dot product, which is equivalent to the sum of the products of each index for each vector
     */
    public static double weightedDot(final Vec w, final Vec x, final Vec y)
    {
        if(w.length() != x.length() || x.length() != y.length())
            throw new ArithmeticException("All 3 vector inputs must have equal lengths");
        
        double sum = 0;
        
        if(x.isSparse() && y.isSparse())
        {
            Iterator<IndexValue> xIter = x.iterator();
            Iterator<IndexValue> yIter = y.iterator();

            IndexValue xiv = xIter.hasNext() ? xIter.next() : badIV;
            IndexValue yiv = yIter.hasNext() ? yIter.next() : badIV;
            
            while(xiv != badIV && yiv != badIV)
            {
                if(xiv.getIndex() < yiv.getIndex())
                    xiv = xIter.hasNext() ? xIter.next() : badIV;
                else if(yiv.getIndex() > xiv.getIndex())
                    yiv = yIter.hasNext() ? yIter.next() : badIV;
                else//on the same page
                {
                    sum += w.get(xiv.getIndex())*xiv.getValue()*yiv.getValue();
                    xiv = xIter.hasNext() ? xIter.next() : badIV;
                    yiv = yIter.hasNext() ? yIter.next() : badIV;
                }
            }
        }
        else if(x.isSparse())
        {
            for(IndexValue iv : x)
            {
                int indx = iv.getIndex();
                sum += w.get(indx)*iv.getValue()*y.get(indx);
            }
        }
        else if(y.isSparse())
            return weightedDot(w, y, x);
        else//all dense
        {
            for(int i = 0; i < w.length(); i++)
                sum += w.get(i)*x.get(i)*y.get(i);
        }
        
        return sum;
    }
}