 
 
 
 
 
 
 
  
When  and
 and 
 
 
Here we need to eliminate the singularity when
 . In order to do so, we skip data points which are zero. 
Then if
. In order to do so, we skip data points which are zero. 
Then if 
 is the number of non-zero data points,
 is the number of non-zero data points, 
 
 
 
where
 is the simple average of the non-zero data points; and of course
 is the simple average of the non-zero data points; and of course
