functions in rays.i - f

             best= form_rays( [x, y, z, theta, phi] )  
          or dirt= form_rays( [x, y, theta] )  
          or internal= form_rays( [cos, sin, y, z, x, r] )  
 
     forms 5-by-nrays, 3-by-nrays, or 6-by-nrays ray representation  
     given individual lists of array coordinates.  The [...]  
     operator builds an nrays-by-5, nrays-by-3, or nrays-by-6  
     array, which form_rays transposes.  The "nrays" may represent  
     zero or more actual dimensions.  
interpreted function, defined at i/rays.i   line 27