atan2

See the current Perl documentation for atan2.

Here is our local, out-dated (pre-5.6) version:

atan2 - arctangent of Y/X

atan2 Y,X

Returns the arctangent of Y/X in the range -PI to PI.

For the tangent operation, you may use the POSIX::tan() function, or use the familiar relation:

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