Program sfwave124 | 1-D finite-difference wave extrapolation 
[SYNOPSIS]
sfwave124 < inp.rsf > out.rsf vel=vel.rsf grad=grad.rsf what=2
[PARAMETERS]
file    | grad | = |   | 	auxiliary input file name
file    | vel | = |   | 	auxiliary input file name
int     | what | =2 |   | 	2nd or 4th order for FD
[DIRECTORY]
user/songxl
