calc_total_links Function

    function calc_total_links(this) result(total_links)
        class(lattice) :: this
        integer :: ind, total_links

        total_links = 0
        do ind = 1, this%get_nsites()
            total_links = total_links + this%get_num_neighbors(ind)
        end do

        total_links = total_links / 2
    end function calc_total_links