sub _get_seed {
    my $self       = shift;
    my $n_bkgd_seq = List::Util::sum( @{ $self->{bkgd_ref}->[0] } );
    my @hd_sum;
    for my $oligo_indice ( 0 .. $#{ $self->{oligo_ref} } ) {
        $hd_sum[$oligo_indice] =
            List::Util::sum( @{ $self->{hd_matrix_ref}->[$oligo_indice] } ); # 476
    }