Program sfvelcon3 | 3-D finite-difference velocity continuation on a helix 
[SYNOPSIS]
sfvelcon3 < inp.rsf > out.rsf adj=y inv=1 nv=nt vel=1.
[PARAMETERS]
bool    | adj | =y |  [y/n] | 	forward or backward continuation 
int     | inv | =1 |   | 	inversion type 
int     | nv | =nt |   | 	velocity steps 
float   | vel | =1. |   | 	initial velocity 
[DIRECTORY]
user/gee
