Pre-Collision PDFs in Macroscopic Quantity Kernels

Added flags to macroscopic_values_getter and macroscopic_values_setter to explicitly use pre-collision PDFs. Required for consistent initialization in the presence of forces.

lbmpy/macroscopic_value_kernels.py

@@ -8,11 +8,11 @@ from lbmpy.advanced_streaming.utility import get_accessor, Timestep
 
 
 def pdf_initialization_assignments(lb_method, density, velocity, pdfs,
-                                   streaming_pattern='pull', timestep=Timestep.BOTH,
+                                   streaming_pattern='pull', previous_timestep=Timestep.BOTH,
                                    set_pre_collision_pdfs=False):
     """Assignments to initialize the pdf field with equilibrium"""
     if isinstance(pdfs, Field):
-        accessor = get_accessor(streaming_pattern, timestep)
+        accessor = get_accessor(streaming_pattern, previous_timestep)
         if set_pre_collision_pdfs:
             field_accesses = accessor.read(pdfs, lb_method.stencil)
         else:
@@ -32,10 +32,10 @@ def pdf_initialization_assignments(lb_method, density, velocity, pdfs,
 
 
 def macroscopic_values_getter(lb_method, density, velocity, pdfs,
-                              streaming_pattern='pull', timestep=Timestep.BOTH,
+                              streaming_pattern='pull', previous_timestep=Timestep.BOTH,
                               use_pre_collision_pdfs=False):
     if isinstance(pdfs, Field):
-        accessor = get_accessor(streaming_pattern, timestep)
+        accessor = get_accessor(streaming_pattern, previous_timestep)
         if use_pre_collision_pdfs:
             field_accesses = accessor.read(pdfs, lb_method.stencil)
         else: