Synopsis
		sfmaxwell_direct_backward < Fv.rsf > Fw1.rsf back=Fw2.rsf rho=Frho.rsf eta=Feta.rsf ef=Fef.rsf eb=Feb.rsf wltf=Fwltf.rsf wltb=Fwltb.rsf nb=30 nt=1000 dt=0.001 fm=20.

This code is only valid with attenuation. No attenuation fails.

Parameters
		file back= auxiliary output file name   dt=0.001 time sampling interval   file eb= auxiliary output file name   file ef= auxiliary output file name   file eta= auxiliary input file name   fm=20. domainant frequency for ricker wavelet   nb=30 thinkness of sponge ABC   nt=1000 number of time steps   file rho= auxiliary input file name   file wltb= auxiliary output file name   file wltf= auxiliary output file name