functions in hex.i - t

             result= track_integ(nlist, transp, selfem, last)  
 
     integrates a transport equation by doing the sums:  
        transparency(i) = transparency(i-1) * TRANSP(i)  
        emissivity(i) = emissivity(i-1) * TRANSP(i) + SELFEM(i)  
     returning only the final values transparency(n) and emissivity(n).  
     The NLIST is a list of n values, so that many transport integrals  
     can be performed simultaneously; sum(NLIST) = numberof(TRANSP) =  
     numberof(SELFEM).  The result is 2-by-dimsof(NLIST).  
     If TRANSP is nil, result is dimsof(NLIST) sums of SELFEM.  
     If SELFEM is nil, result is dimsof(NLIST) products of TRANSP.  
     TRANSP and SELFEM may by 2D to do multigroup integrations  
     simultaneously.  By default, the group dimension is first, but  
     if LAST is non-nil and non-zero, the group dimension is second.  
     In either case, the result will be ngroup-by-2-by-dimsof(NLIST).  
     track_solve is the higher-level interface.  
interpreted function, defined at i0/hex.i   line 290  

             nlist= track_reduce(c, s)  
          or nlist= track_reduce(c, s, rays, slimits)  
 
     compresses the C and S returns from the tracking routines (see  
     hex5_track) to the following form:  
       [cell1,cell2,cell3,..., cell1,cell2,cell3,..., ...]  
       [s1-s0,s2-s1,s3-s2,..., s1-s0,s2-s1,s3-s2,..., ...]  
     returning nlist as  
       [#hits, #hits, ...]  
     In this form, any negative #hits are combined with the preceding  
     positive values, and #hits=1 (indicating a miss) appear as #hits=0  
     in nlist.  Hence, nlist always has exactly Nrays elements.  
     If RAYS is supplied, it is used to force the dimensions of the  
     returned nlist to match the dimensions of RAYS (the value of RAYS  
     is never used).  The RAYS argument need not have the trailing 2  
     dimension, so if you specified RAYS as [P,Q] if the call to  
     hex5_track, you can use just P or Q as the RAYS argument to  
     track_reduce.  
     If SLIMITS is supplied, it should be [smin,smax] or [smin,smax]-  
     by-dimsof(nlist) in order to reject input S values outside the  
     specified limits.  The C list will be culled appropriately, and  
     the first and last returned ds values adjusted.  
     With a non-zero flip= keyword, the order of the elements of  
     C and S within each group of #hits is reversed, so that a  
     subsequent track_solve will track the ray backwards.  If you  
     use this, both the ray direction input to the tracking routine  
     and any SLIMITS argument here should refer to the reverse of  
     the ray you intend to track.  
interpreted function, defined at i0/hex.i   line 156  

             result= track_solve(nlist, c, s, akap, ekap, last)  
 
     integrates a transport equation for NLIST, C, and S returned  
     by track_reduce (and optionally c_adjust).  The RAYS argument  
     is used only to set the dimensions of the result.  AKAP and  
     EKAP are mesh-sized arrays of opacity and emissivity, respectively.  
     They may have an additional group dimension, as well.  The  
     units of AKAP are 1/length (where length is the unit of S),  
     while EKAP is (spectral) power per unit area (length^2), where  
     the power is what ever units you want the result in.  The  
     emission per unit volume of material is EKAP*AKAP; an optically  
     thick block of material emits EKAP per unit surface.  
     The NLIST is a list of n values, so that many transport integrals  
     can be performed simultaneously; sum(NLIST) = numberof(AKAP) =  
     numberof(EKAP).  The result is 2-by-dimsof(NLIST), where the  
     first element of the first index is the transmission fraction  
     through the entire ray path, and the second element of the  
     result is the self-emission along the ray, which has the same  
     units as EKAP.  
     If EKAP is nil, result is dimsof(NLIST) -- exactly the same as  
     the transparency (1st element of result) when both EKAP and AKAP  
     are specified.  
     If AKAP is nil, result is dimsof(NLIST).  In this case, EKAP  
     must have units of emission per unit volume instead of per unit  
     area; the result will be the sum of EKAP*S along each ray.  
     AKAP and EKAP may by 2D to do multigroup integrations  
     simultaneously.  By default, the group dimension is first, but  
     if LAST is non-nil and non-zero, the group dimension is last.  
     In either case, the result will be ngroup-by-2-by-dimsof(NLIST).  
     To use in conjuction with hex5_track, one might do this:  
        c= hex5_track(mesh, rays, s);  
        nlist= track_reduce(c, s, rays);  
        c_adjust, c, mesh;  // if necessary  
        result= track_solve(nlist, c, s, akap, ekap);  
interpreted function, defined at i0/hex.i   line 349