VEL2STIFFb - Transforms VELocities, densities, and Thomsen or Sayers   
              parameters to elastic STIFFnesses 			

 vel2stiffb  nx=  nz=  vpfile= vsfile= rhofile=  epsfile= 		
		deltafile= gammafile=  c11_file= c13_file= c33_file= 	
		c44_file=[] c66_file=[]					

 Required parameters:							
 vpfile=	file with P-wave velocities				
 vsfile=	file with S-wave velocities				
 rhofile=	file with densities					

 Optional Parameters:							
 epsfile=	file with Thomsen/Sayers epsilon		       	
 deltafile=	file with Thomsen/Sayers delta		       	 	
 gammafile=	file with Thomsen/Sayers gamma	       		 	

 parameters=1  (1) Thomsen parameters, (0) Sayers parameters(see below)

 nx=101	number of x samples (2nd dimension)			
 nz=101	number of z samples (1st dimension)			

 Notes: 								
 Transforms velocities, density and Thomsen/Sayers parameters	      	
 epsilon,delta and gamma into elastic stiffness coefficients.		
 If only P-wave, S-wave velocities and density is given as input,	
 the model is assumed to be isotropic.					
 If files containing Thomsen/Sayers parameters are given, the model    
 will be assumed to have VTI symmetry.		 			



  Coded:
  CWP: Sverre Brandsberg-Dahl 1999

  Extended:
  CWP: Stig-Kyrre Foss 2001
  - to include the option to use the parameters by Sayers (1995) 
  instead of the Thomsen parameters

 Sayers, C. M.: Simplified anisotropy parameters for transversely 
 isotropic sedimentary rocks. Geophysics 1995, pages 1933-1935.