EFUN: atan

SYNTAX:
float atan( x );
  float x;

DESCRIPTION:
Calculates the arctangent of x.

RETURN VALUE:
The value of atan( x ) is returned (varies between -0.5*PI and 0.5*PI).

SEE ALSO:
tan
asin
acos

EXAMPLE:
float x;

x = atan( 0 );
// x has now a value of 0.
