public double correlation(final Histogram first, final int displacement, final Histogram second) {
// number of bins (classes)
final int numberOfClasses = first.getNumberOfClasses();
// start value
final double start = first.getStart();
// stop value
final double stop = first.getStop();
// classWidth
final double classWidth = first.getClassWidth();
int actualDisplacement = displacement;
// make displacement positive
if (actualDisplacement < 0) {
actualDisplacement =
((actualDisplacement % numberOfClasses) + numberOfClasses) % numberOfClasses;
}
double distance = 0.0;
for (double current = start + classWidth / 2; current <= stop; current += classWidth) {
final double displacedValue =
(current + actualDisplacement * classWidth) % (numberOfClasses * classWidth);
distance += Math.pow(first.getCount(current) * second.getCount(displacedValue), 0.5);
}
return Math.log(distance);
}
