Synopsis
		sffreqreg < in.rsf > out.rsf mask=mask.rsf nw= dw= w0=0. rect=10 niter=100 verb=n

Parameters
		float dw= frequency step   string mask= auxiliary input file name   int niter=100 number of inversion iterations   int nw= number of frequencies   int rect=10 smoothing radius   bool verb=n [y/n] verbosity flag   float w0=0. first frequency