Program sfwavefft1 | 1-D finite-difference wave extrapolation 
[SYNOPSIS]
sfwavefft1 < inp.rsf > out.rsf vel=vel.rsf grad=grad.rsf opt=y dt= nt=
[PARAMETERS]
float   | dt | = |   | 	
file    | grad | = |   | 	auxiliary input file name
int     | nt | = |   | 	if y, determine optimal size for efficiency 
bool    | opt | =y |  [y/n] | 	
file    | vel | = |   | 	auxiliary input file name
[DIRECTORY]
user/songxl
