Program sfwave1 | 1-D finite-difference wave extrapolation 
[SYNOPSIS]
sfwave1 < inp.rsf > out.rsf vel=vel.rsf grad=grad.rsf
[PARAMETERS]
file    | grad | = |   | 	auxiliary input file name
file    | vel | = |   | 	auxiliary input file name
[DIRECTORY]
user/songxl
