====== Description ======
The atan node returns the arc tangent of the value of its child-node.

====== Constraints ======
  * Minimum number of child-nodes: 1
  * Maximum number of child-nodes: 1
  * Valid input range: no constraints
  * Output range: -<m>pi</m>/2 to +<m>pi</m>/2 (radians) 

====== Calculus ======
The atan node's value is the arc tangent, in radians, of the value of its child-node.

For valid value<sub>1</sub>:

value = tan<sup>-1</sup>(value<sub>1</sub>)