perldoc > atan2(3)

• atan2(Y,X) — Returns the arctangent of Y/X in the range -PI to PI.

For the tangent operation, you may use the "Math::Trig::tan" function, or use the familiar relation:

sub tan { sin($_[0]) / cos($_[0])  }

The return value for "atan2(0,0)" is implementation-defined; consult your atan2(3) manpage for more information.

Portability issues: "atan2" in perlport.