private void rescale(long newLandmarkInSeconds) {
// rescale the weights based on a new landmark to avoid numerical overflow issues
final double factor = Math.exp(-alpha * (newLandmarkInSeconds - landmarkInSeconds));
weightedCount *= factor;
postOrderTraversal(
root,
new Callback() {
@Override
public boolean process(Node node) {
double oldWeight = node.weightedCount;
node.weightedCount *= factor;
if (oldWeight >= ZERO_WEIGHT_THRESHOLD && node.weightedCount < ZERO_WEIGHT_THRESHOLD) {
--nonZeroNodeCount;
}
return true;
}
});
landmarkInSeconds = newLandmarkInSeconds;
}
private double weight(long timestamp) {
return Math.exp(alpha * (timestamp - landmarkInSeconds));
}