Synopsis
		sfpspig < inp.rsf > out.rsf vel=vel.rsf grad=grad.rsf opt=y dt= nt= nv= lmdv= lmdvx=

Parameters
		float dt=   file grad= auxiliary input file name   float lmdv=   float lmdvx= if y, determine optimal size for efficiency   int nt=   int nv=   bool opt=y [y/n]   file vel= auxiliary input file name