Theta

#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';
use Math::Trig;
sub theta {
  my ($x1, $y1, $x2, $y2) = @_;
  $x1 = deg2rad $x1;
  $y1 = deg2rad $y1;
  $x2 = deg2rad $x2;
  $y2 = deg2rad $y2;
  my $theta = rad2deg(
    acos(1 - (1 / 2) *
      (
        (cos($y1) * sin($x1) - cos($y2) * sin($x2)) ^ 2 +
        (cos($y1) * cos($x1) - cos($y2) * cos($x2)) ^ 2 +
        (sin($y1) - sin($y2)) ^ 2
      )
    )
  );
  return $theta;
}
my $data = [];
my $result = [];
while (<>) {
  chomp;
  my @d = split;
  push @$data, \@d;
}
my $size = scalar @$data;
for (my $i = 0; $i < $size; $i++) {
  for (my $j = $i + 1; $j < $size; $j++) {
    my $r = [$data->[$i][0], $data->[$i][1], $data->[$j][0], $data->[$j][1]];
    push @$r, theta @$r;
    push @$result, $r;
  }
}
@$result = sort { $a->[4] <=> $b->[4] } @$result;
foreach my $r (@$result) {
  say join "\t", @$r;
}