Synopsis
		sfpspifb1 < inp.rsf > out.rsf vel=vel.rsf grad=grad.rsf opt=y dt= nt= nv= nb=20 abc=0

Parameters
		int abc=0 absorbing boundary condition 1: cos 0: exp   float dt=   file grad= auxiliary input file name   int nb=20   int nt=   int nv=   bool opt=y [y/n]   file vel= auxiliary input file name