A HistogramNd is an n-dimensional histogram that tracks up to four kinds of values: 1) values in the center of the distribution 2) values to the left of the center of the distribution (lower tail) 3) values to the right of the center of the distribution (upper tail) 4) values outside the other areas
Note: the last three classifications may not be present depending upon the makeup of the input data.
@author Barry DeZonia