GitLab

As shown in the literature it is not a particularly good idea to define the relaxation rate of the moments by the ordering. In fact, there are different things that need to be considered. The most prominent one is the isotropy condition. This means that moments that are rotated forms of others should be relaxed with the same relaxation rate. The idea is defined here.

Furthermore, the big problem with MRT-like methods is that moments are not statistically independent. Thus moments sharing information with each other should not be relaxed with different relaxation rates. This could lead to another approach when thinking about the grouping of the relaxation rates.