code: static double quantile(double index, double previousIndex, double nextIndex, double previousMean, double nextMean) {
          final double delta = nextIndex - previousIndex;
          final double previousWeight = (nextIndex - index) / delta;
          final double nextWeight = (index - previousIndex) / delta;
          return previousMean * previousWeight + nextMean * nextWeight;
      }
docs: Computes an interpolated value of a quantile that is between two centroids.
  
  Index is the quantile desired multiplied by the total number of samples - 1.
  
  @param index              Denormalized quantile desired
  @param previousIndex      The denormalized quantile corresponding to the center of the previous centroid.
  @param nextIndex          The denormalized quantile corresponding to the center of the following centroid.
  @param previousMean       The mean of the previous centroid.
  @param nextMean           The mean of the following centroid.
  @return  The interpolated mean.