Roots of bessj0:
                    x            f(x)
root   1       2.404827      -0.000001
root   2       5.520077       0.000000
root   3       8.653729       0.000000
root   4      11.791534       0.000000
root   5      14.930918       0.000000
root   6      18.071066       0.000000
root   7      21.211636       0.000000
root   8      24.352472       0.000000
root   9      27.493477       0.000000
root  10      30.634607       0.000000
root  11      33.775822       0.000000
root  12      36.917095       0.000000
root  13      40.058426       0.000000
root  14      43.199787      -0.000001
root  15      46.341187       0.000000
root  16      49.482613       0.000000