Fix split error

When the split algorithm is used in combination with an output field a KeyError error was thrown. This error arises because the split simplification is added before the output fields were added to the collision rule. Thus, the simplification strategy did not know about the additional assignments.

The error is was fixed by reordering the code in createfunctions.py.

lbmpy/creationfunctions.py

@@ -322,6 +322,11 @@ def create_lb_collision_rule(lb_method=None, optimization={}, **kwargs):
     else:
         collision_rule = lb_method.get_collision_rule(keep_rrs_symbolic=keep_rrs_symbolic)
 
+    if params['output'] and params['kernel_type'] == 'stream_pull_collide':
+        cqc = lb_method.conserved_quantity_computation
+        output_eqs = cqc.output_equations_from_pdfs(lb_method.pre_collision_pdf_symbols, params['output'])
+        collision_rule = collision_rule.new_merged(output_eqs)
+
     if opt_params['simplification'] == 'auto':
         simplification = create_simplification_strategy(lb_method, split_inner_loop=split_inner_loop)
     else:
@@ -358,11 +363,6 @@ def create_lb_collision_rule(lb_method=None, optimization={}, **kwargs):
     if cse_global:
         collision_rule = sympy_cse(collision_rule)
 
-    if params['output'] and params['kernel_type'] == 'stream_pull_collide':
-        cqc = lb_method.conserved_quantity_computation
-        output_eqs = cqc.output_equations_from_pdfs(lb_method.pre_collision_pdf_symbols, params['output'])
-        collision_rule = collision_rule.new_merged(output_eqs)
-
     return collision_rule