SUFDMOD2 - Finite-Difference MODeling (2nd order) for acoustic wave equation

 sufdmod2 <vfile >wfile nx= nz= tmax= xs= zs= [optional parameters]	

 Required Parameters:							
 <vfile		file containing velocity[nx][nz]		
 >wfile		file containing waves[nx][nz] for time steps	
 nx=			number of x samples (2nd dimension)		
 nz=			number of z samples (1st dimension)		
 xs=                   x coordinates of source, or, alternatively, the name
                       of a file that contains the x- and z-coordinates,
                       with the number of pairs as the first record and
                       the actual pairs of (x,z) locations following.  
 zs=			z coordinates of source				
 sstrength=1.0		strength of source				
 tmax=			maximum time					

 Optional Parameters:							
 nt=1+tmax/dt		number of time samples (dt determined for stability)
 mt=1			number of time steps (dt) per output time step	

 dx=1.0		x sampling interval				
 fx=0.0		first x sample					
 dz=1.0		z sampling interval				
 fz=0.0		first z sample					

 fmax = vmin/(10.0*h)	maximum frequency in source wavelet		
 fpeak=0.5*fmax	peak frequency in ricker wavelet		

 dfile=		input file containing density[nx][nz]		
 vsx=			x coordinate of vertical line of seismograms	
 hsz=			z coordinate of horizontal line of seismograms	
 vsfile=		output file for vertical line of seismograms[nz][nt]
 hsfile=		output file for horizontal line of seismograms[nx][nt]
 ssfile=		output file for source point seismograms[nt]	
 verbose=0		=1 for diagnostic messages, =2 for more		

 abs=1,1,1,1		Absorbing boundary conditions on top,left,bottom,right
 			sides of the model. 				
 		=0,1,1,1 for free surface condition on the top		

 Notes:								

 This program uses the traditional explicit second order differencing	
 method. 								



 Authors:  CWP:Dave Hale
           CWP:modified for SU by John Stockwell, 1993.


 Trace header fields set: sx, gx, ns, delrt, tracl, tracr, offset, d1, d2,
                          sdepth, trid

 Modifications: Tony Kocurko (TK:)
                Memorial University in Newfoundland and Labrador
                - Allow user to supply the name of a file containing
                  shot point locations, rather than supplying them
                  as values to the xs= and zs= command line arguments.
                - Correct the calculation of izs[is].