functions in drat.i - i

             integ_flat(opac, source, rays, mesh, slimits)  
          or integ_flat(opac, source, ray_paths)  
 
     returns ngroup-by-2-by-nrays result, where result(,1,..) is  
     the transparency factors, and result(,2,..) is the self-emission  
     for each group on each ray.  The input OPAC and SOURCE are the  
     opacity (an inverse length) and the source function (a specific  
     intensity).  They are mesh-by-ngroups zone centered arrays.  The  
     result has the same units as SOURCE.  
     In the second form, RAY_PATHS was returned by the track_rays  
     function.  
interpreted function, defined at i0/drat.i   line 1109  

             integ_linear(opac, source, rays, mesh, slimits)  
          or integ_linear(opac, source, ray_paths)  
 
     returns ngroup-by-2-by-nrays result, where result(,1,..) is  
     the transparency factors, and result(,2,..) is the self-emission  
     for each group on each ray.  The input OPAC and SOURCE are the  
     opacity (an inverse length) and the source function (a specific  
     intensity).  They are mesh-by-ngroups arrays; OPAC is zone centered,  
     while SOURCE is point centered (using pcen_source).  The result  
     has the same units as SOURCE.  
     In the second form, RAY_PATHS was returned by the track_rays  
     function.  
     The integ_linear routine assumes that the SOURCE function varies  
     linearly between the entry and exit points from each zone.  This  
     assumption is poor near the turning point, and causes the result  
     to be a discontinuous function of the ray coordinates, unlike the  
     integ_flat result.  
interpreted function, defined at i0/drat.i   line 1152  

             is_present(get_vars(f), name)  
 
     returns 1 if variable NAME is present in file F, 0 if not.  
interpreted function, defined at i0/drat.i   line 889