Fix implizit force model

lbmpy/methods/centeredcumulant/force_model.py

-from lbmpy.forcemodels import AbstractForceModel
+from lbmpy.forcemodels import AbstractForceModel, default_velocity_shift
 
 
 #   =========================== Centered Cumulant Force Model ==========================================================
@@ -22,3 +22,6 @@ class CenteredCumulantForceModel(AbstractForceModel):
 
     def __call__(self, lb_method):
         raise Exception('This force model does not provide a forcing term.')
+
+    def equilibrium_velocity_shift(self, density):
+        return default_velocity_shift(density, self.symbolic_force_vector)

lbmpy/methods/momentbased/entropic_eq_srt.py

@@ -10,6 +10,7 @@ class EntropicEquilibriumSRT(AbstractLbMethod):
     """Equilibrium from 'Minimal entropic kinetic models for hydrodynamics'
     Ansumali, S. ; Karlin, I. V;  Öttinger, H. C, (2003)
     """
+
     def __init__(self, stencil, relaxation_rate, force_model, conserved_quantity_calculation):
         super(EntropicEquilibriumSRT, self).__init__(stencil)
 
@@ -91,7 +92,4 @@ def create_srt_entropic(stencil, relaxation_rate, force_model, compressible):
         raise NotImplementedError("entropic-srt only implemented for compressible models")
     density_velocity_computation = DensityVelocityComputation(stencil, compressible, force_model)
 
-
-
-
     return EntropicEquilibriumSRT(stencil, relaxation_rate, force_model, density_velocity_computation)