Reimplement create_staggered_kernel

create_staggered_kernel now takes a list of assignments to staggered fields and otherwise behaves like create_kernel. I have included a diffusion equation test case in both D2Q5 and D2Q9. Putting vectorial/tensorial quantities on the staggered points also works.

This merge requests break API compatibility with the previous create_staggered_kernel.

Fixes #16 (closed). My next step is to implement automatic FV discretization.

Build of dependent projects (pygrandchem, pystencils_walberla) passes as per https://i10git.cs.fau.de/pycodegen/pycodegen/merge_requests/6.

pystencils/kernelcreation.py

@@ -213,16 +213,15 @@ def create_staggered_kernel(assignments, gpu_exclusive_conditions=False, **kwarg
     """
     assert 'iteration_slice' not in kwargs and 'ghost_layers' not in kwargs
 
-    subexpressions = ()
     if isinstance(assignments, AssignmentCollection):
         subexpressions = assignments.subexpressions + [a for a in assignments.main_assignments
                                                        if type(a.lhs) is not Field.Access
-                                                       and not FieldType.is_staggered(a.lhs.field)]
+                                                       or not FieldType.is_staggered(a.lhs.field)]
         assignments = [a for a in assignments.main_assignments if type(a.lhs) is Field.Access
                        and FieldType.is_staggered(a.lhs.field)]
     else:
         subexpressions = [a for a in assignments if type(a.lhs) is not Field.Access
-                          and not FieldType.is_staggered(a.lhs.field)]
+                          or not FieldType.is_staggered(a.lhs.field)]
         assignments = [a for a in assignments if type(a.lhs) is Field.Access 
                        and FieldType.is_staggered(a.lhs.field)]
     if len(set([tuple(a.lhs.field.staggered_stencil) for a in assignments])) != 1: