atan2

• 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.