4.4 Compiler macros

Some of the modules of the CO5BOLD code (with suffix ``.F90'') employ compiler macros to switch between code versions during compile time. Typically you define at least one of the three switches rhd_r01, rhd_r02, or rhd_r03 to choose a radiation transport module. The others have reasonable default values. To find the combination with the optimal performance, you should look into Sect.4.5 The macros are sorted into different categories: Some activate a certain feature (like a radiation transport module or the dust module). They have to be selected by the user (typically via environment variables and the configure script, see Sect.4.3) each time the code is compiled for a certain purpose. Other macros are meant to improve the performance by offering the choice between e.g. different loop structures or case distinctions. These macros are set by the configure script to the best knowledge of the author(s). Ideally, they should be checked and modified if necessary each time CO5BOLD is compiled on a new machine. It should be save to modify these settings: the results between runs with different settings should only differ slightly due to round-off errors. Some macros select between different numerical approximations. A change here should be visible in a (more or less drastic) change of the results of a simulation. Usually, the default values should be accepted. Other settings typically only exist to allow the comparison with older versions of CO5BOLD or because there are new developments going on which have not yet managed to become the default. A couple of macros only activate timing measurements and result in additional output. Some of them are not thread-save und should only be activated for runs on one thread (as done by the configure script). It is always save to switch any of them off (by removing or undefining them). The macros in the category test mark parts of code under development. The default values should only be changed with great care (typically by the author of that code segment). The configure script does not touch these settings.