some fixes for lbmpy vectorization

pystencils/cpu/vectorization.py

@@ -210,6 +210,8 @@ def insert_vector_casts(ast_node):
                 # special treatment for the unary minus: make sure that the -1 has the same type as the argument
                 dtype = int
                 for arg in expr.args[1:]:
+                    if type(arg) is sp.Pow:
+                        arg = arg.args[0]
                     if type(arg) is vector_memory_access and arg.dtype.base_type.is_float():
                         dtype = arg.dtype.base_type.numpy_dtype.type
                     elif type(arg) is TypedSymbol and type(arg.dtype) is VectorType and arg.dtype.base_type.is_float():

pystencils/simp/assignment_collection.py

@@ -437,9 +437,10 @@ class AssignmentCollection:
 class SymbolGen:
     """Default symbol generator producing number symbols ζ_0, ζ_1, ..."""
 
-    def __init__(self, symbol="xi"):
+    def __init__(self, symbol="xi", dtype=None):
         self._ctr = 0
         self._symbol = symbol
+        self._dtype = dtype
 
     def __iter__(self):
         return self
@@ -447,4 +448,6 @@ class SymbolGen:
     def __next__(self):
         name = f"{self._symbol}_{self._ctr}"
         self._ctr += 1
+        if self._dtype is not None:
+            return pystencils.TypedSymbol(name, self._dtype)
         return sp.Symbol(name)