Synopsis
		sfnmodips < cmp.rsf > dip.rsf offset=offset.rsf half=y nv= v0= dv= CDPtype= slowness=n squared=n h0=0. extend=4

Parameters
		int CDPtype=   float dv= step in velocity   int extend=4 trace extension   float h0=0. reference offset   bool half=y [y/n] if y, the second axis is half-offset instead of full offset   int nv= number of velocities   string offset= auxiliary input file name   bool slowness=n [y/n] if y, use slowness instead of velocity   bool squared=n [y/n] if y, the slowness or velocity is squared   float v0= first velocity