Synopsis
		sfsstep2 < in.rsf > out.rsf slowness=vel.rsf inv=n verb=n eps=0.01 nt=1 nr=1 padx=0 pady=0 dt=0.004 nw= dw= w0=0.

Parameters
		float dt=0.004 time error   float dw= Frequency sampling (for modeling)   float eps=0.01 stability parameter   bool inv=n [y/n] If y, modeling; if n, migration   int nr=1 maximum number of references   int nt=1 taper size   int nw= Length of frequency axis (for modeling)   int padx=0 cross-line padding   int pady=0 in-line padding   file slowness= auxiliary input file name   bool verb=n [y/n] verbosity flag   float w0=0. Frequency origin (for modeling)