decide_num_to_spawn Subroutine

    subroutine decide_num_to_spawn(parent_pop, av_spawns_per_walker, nspawn)

        real(dp), intent(in) :: parent_pop
        real(dp), intent(in) :: av_spawns_per_walker
        integer, intent(out) :: nspawn
        real(dp) :: prob_extra_walker, r

        nspawn = abs(int(parent_pop * av_spawns_per_walker))
        if (abs(abs(parent_pop * av_spawns_per_walker) - real(nspawn, dp)) > 1.e-12_dp) then
            prob_extra_walker = abs(parent_pop * av_spawns_per_walker) - real(nspawn, dp)
            r = genrand_real2_dSFMT()
            if (prob_extra_walker > r) nspawn = nspawn + 1
        end if

    end subroutine decide_num_to_spawn