Reference: atan2 (Perl in a Nutshell)

atan2

atan2 
y
, 
x

Returns the arctangent of y / x in the range - [pi] to [pi] . A quick way to get an approximate value of [pi] is to say:

$pi = atan2(1,1) * 4;

For the tangent operation, you may use the


POSIX::tan()

function, or use the familiar relation:

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