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      11.791533       0.000000
root   5      14.930930      -0.000003
root   6      18.071054      -0.000002
root   7      21.211639       0.000000
root   8      24.352465      -0.000001
root   9      27.493486      -0.000001
root  10      30.634581      -0.000004
root  11      33.775833      -0.000002
root  12      36.917088      -0.000001
root  13      40.058434      -0.000001
root  14      43.199783      -0.000001
root  15      46.341213      -0.000003
root  16      49.482594      -0.000002