3.16.3. Short characteristics¶

Short characteristics radiative transfer solvers typically solve the radiative transfer equations across only a single cell (or in some cases even a fraction of a cell) at a time. In three dimensions one can nevertheless achieve excellent performance, by parallelizing over perpendicular directions – effectively solving for the radiation over parallel planes, progressing from one plane to the next, starting from a boundary where values are known, either from physical boundary conditions, or from boundary values taken from an adjacent (“up-stream”) domain.

Because one is looping over two redundant directions, it is possible to significantly reduce the cost, since it allows the compiler to use loop vectorization.

The solvers/rt/short_characteristics/ directory contains the following modules, used to perform various parts of such solutions::

radau_mod.f90                 ! Radau integration -- a modified Gauss integration
rt_integral_mod.f90           ! integral method solver
rt_mod.f90                    ! RT data type definitions
rt_nbors.f90                  ! RT neighbor setup
rt_solver_mod.f90             ! RT solver data type