===== Arc Tangent ======

==== atan( a ) ====

Return the arc tangent of a.

=== Description ===

<code>atan( a )</code>

Return the arc tangent of a.

=== Parameters ===

| ''a'' | Angle in radians [-1 to +1]|

=== Return value ===

arc tangent of a

=== Example usage ===

<code>atan( 1 )</code>

Returns 0.7854...