Fixed extraction of common srt eq term

lbmpy/methods/momentbased/momentbasedsimplifications.py

@@ -43,7 +43,7 @@ def factor_relaxation_rates(cr: LbmCollisionRule):
     """
     sh = cr.simplification_hints
     assert 'relaxation_rates' in sh, "Needs simplification hint 'relaxation_rates': Sequence of relaxation rates"
-    if len(sh['relaxation_rates']) > 19:  # heuristics, works well if there is a small number of relaxation rates
+    if len(set(sh['relaxation_rates'])) > 19:  # heuristics, works well if there is a small number of relaxation rates
         return cr
 
     relaxation_rates = sp.Matrix(sh['relaxation_rates']).atoms(sp.Symbol)
@@ -385,10 +385,15 @@ def __get_common_quadratic_and_constant_terms(cr: LbmCollisionRule):
         t = t.subs({ft: 0 for ft in sh['force_terms']})
 
     weight = t
+    weight = weight.subs(sh['density_deviation'], 1)
+    weight = weight.subs(sh['density'], 1)
 
     for u in sh['velocity']:
         weight = weight.subs(u, 0)
-    weight = weight / sh['density']
+    # weight = weight / sh['density']
     if weight == 0:
         return None
+
+    # t = t.subs(sh['density_deviation'], 0)
+
     return t / weight

lbmpy_tests/test_srt_trt_simplifications.py

@@ -31,20 +31,34 @@ def check_method(method, limits_default, limits_cse):
     assert ops_cse['divs'] <= limits_cse[2]
 
 
-def test_simplifications_srt_d2q9_incompressible():
+def test_simplifications_srt_d2q9_incompressible_regular():
     omega = sp.symbols('omega')
     method = create_srt(LBStencil(Stencil.D2Q9), omega, compressible=False,
-                        equilibrium_order=2)
-    check_method(method, [53, 46, 0], [57, 38, 0])
+                        zero_centered=False, equilibrium_order=2)
+    check_method(method, [53, 46, 0], [53, 38, 0])
+
+
+def test_simplifications_srt_d2q9_incompressible_zc():
+    omega = sp.symbols('omega')
+    method = create_srt(LBStencil(Stencil.D2Q9), omega, compressible=False,
+                        zero_centered=True, delta_equilibrium=True, equilibrium_order=2)
+    check_method(method, [53, 46, 0], [53, 38, 0])
 
 
-def test_simplifications_srt_d2q9_compressible():
+def test_simplifications_srt_d2q9_compressible_regular():
     omega = sp.symbols('omega')
     method = create_srt(LBStencil(Stencil.D2Q9), omega, compressible=True,
                         equilibrium_order=2)
     check_method(method, [53, 58, 1], [53, 42, 1])
 
 
+def test_simplifications_srt_d2q9_compressible_zc():
+    omega = sp.symbols('omega')
+    method = create_srt(LBStencil(Stencil.D2Q9), omega, compressible=True,
+                        zero_centered=True, delta_equilibrium=True, equilibrium_order=2)
+    check_method(method, [54, 58, 1], [54, 42, 1])
+
+
 def test_simplifications_trt_d2q9_incompressible():
     o1, o2 = sp.symbols("omega_1 omega_2")
     method = create_trt(LBStencil(Stencil.D2Q9), o1, o2, compressible=False)