Program sftrace2 | 2-D multiple arrivals by cell ray tracing. 
[SYNOPSIS]
sftrace2 < vel.rsf > outp.rsf size=size.rsf grid=grid.rsf na=60 da=3.1 a0=-90. maxsplit=10 minx=0.5*dx maxx=2.*dx mina=0.5*da maxa=2.*da vel=y order=3 lsint=n
[PARAMETERS]
float   | a0 | =-90. |   | 	initial angle (in degrees) 
float   | da | =3.1 |   | 	angle increment (in degrees) 
file    | grid | = |   | 	auxiliary output file name
bool    | lsint | =n |  [y/n] | 	if use least-squares interpolation 
float   | maxa | =2.*da |   | 	
int     | maxsplit | =10 |   | 	maximum splitting for adaptive grid 
float   | maxx | =2.*dx |   | 	
float   | mina | =0.5*da |   | 	
float   | minx | =0.5*dx |   | 	parameters for adaptive grid 
int     | na | =60 |   | 	number of angles 
int     | order | =3 |   | 	velocity interpolation order 
file    | size | = |   | 	auxiliary output file name
bool    | vel | =y |  [y/n] | 	y: velocity, n: slowness 
[DIRECTORY]
user/fomels
