====== Description ======

The ave-nz (average-non zero) node calculates the average value of its child-nodes which are not zero.

====== Constraints ======

  * Minimum number of child-nodes: 1
  * Maximum number of child-nodes: no limit

====== Calculus ======
 <m>value=sum{i=1}{n}{value_{i}}/n_nz</m> where n<sub>nz</sub> = count of non-zero nodes