| The SimpleX method for solving the equations of time-dependent radiative transfer is based on photon transport on an unstructured Voronoi-Delaunay grid. It was devised by Ritzerveld and Icke, coded and extensively tested by Ritzerveld, and extended by him and by Paardekooper to include transport through optically active media, in particular ionisation/recombination, and by Kruip for astrochemistry. SimpleX solves these equations with a view towards astrophysical applications. A case in point is the re-ionisation of the Universe, a crucial phase in the formation of cosmic structure. Comparison of the results with those of other methods in the Cosmological Code Comparison project, led by prof. Ilian Iliev, showed that SimpleX is very versatile and extremely fast. The mathematical properties and sources of (systematic) errors in the algorithm were investigated by Kruip, who modified and extended the code in order to take these findings into account. The stationary case of this type of transport was analyzed by Icke in the form of a Markov process, serving as mathematical justification for the method. Kruip and Icke are applying this procedure to some practical cases. SimpleX was designed to be parallel, but the parallelization must now be implemented throughout. The main challenge and innovation consists of engineering a level of ?fine-grained? parallelization necessary to take proper account of the ?optically or chemically active? regions in the simulation volume. |
