Added reference to MRT

lbmpy/methods/creationfunctions.py

@@ -396,6 +396,15 @@ def create_mrt_orthogonal(stencil, relaxation_rate_getter=None, maxwellian_momen
             [x * y * z]
         ]
     elif stencils_have_same_entries(stencil, get_stencil("D3Q19")):
+        # This MRT variant mentioned in the dissertation of Ulf Schiller 
+        # "Thermal fluctuations and boundary conditions in the lattice Boltzmann method" (2008), p. 24ff
+        # There are some typos in the moment matrix on p.27
+        # The here implemented ordering of the moments is however different from that reference (Eq. 2.61-2.63)
+        # The moments are weighted-orthogonal (Eq. 2.58)
+        
+        # Further references:
+        # Duenweg, B., Schiller, U. D., & Ladd, A. J. (2007). Statistical mechanics of the fluctuating lattice Boltzmann equation. Physical Review E, 76(3)
+        # Chun, B., & Ladd, A. J. (2007). Interpolated boundary condition for lattice Boltzmann simulations of flows in narrow gaps. Physical review E, 75(6)
         sq = x ** 2 + y ** 2 + z ** 2
         nested_moments = [
             [one, x, y, z],  # [0, 3, 5, 7]