sub sum($) {
    my $listref = $_[0];
    my $sum = 0;
    map { $sum += $_ } @{$listref};
    return $sum;
}

sub avg($) {
    my $listref = $_[0];
    sum($listref)/@{$listref};
}

sub rms($) {
    my $listref = $_[0];
    sqrt(sum([map{(avg($listref)-$_)**2}@{$listref}])/@{$listref});
}