sub my_gdc1 {
  use POSIX 'ceil';
  my $n = shift;
  my $discrete = ceil($n ** (1/3));
  my @colors = ([1,1,1]);
  for my $i (1..$n-1) {
    push @colors, [map {1-($_%$discrete)/$discrete}
      $i/($discrete**2),
      $i/$discrete,
      $i];
  }
  \@colors;
}