Roots of bessj0:
                    x            f(x)
root   1       2.404826       0.000000
root   2       5.520078       0.000000
root   3       8.653728       0.000000
root   4      11.791534       0.000000
root   5      14.930917       0.000000
root   6      18.071068       0.000001
root   7      21.211637       0.000000
root   8      24.352474       0.000000
root   9      27.493481       0.000000
root  10      30.634600      -0.000001
root  11      33.775822       0.000000
root  12      36.917095       0.000000
root  13      40.058430       0.000000
root  14      43.199791       0.000000
root  15      46.341187       0.000000
root  16      49.482609       0.000000