Program sfeno2 | Convert velocity to slowness and compute gradient using ENO interpolation 
[SYNOPSIS]
sfeno2 < vel.rsf > out.rsf order=3 is_inverse=1
[PARAMETERS]
bool    | is_inverse | =1 |  [y/n] | 	make vel to slowness 
int     | order | =3 |   | 	interpolation order 
[DIRECTORY]
user/fomels
