Remove floor, ceiling for integer symbols

Original Intent

Allow optimizations by SymPy when we know that a TypedSymbol is_integer or is_real (e.g. drop rounding functions).

We can deduce some of those properties with Numpy's type system (https://docs.scipy.org/doc/numpy-1.13.0/reference/arrays.scalars.html). We have to be careful since all the is_* methods have ternary logic (True, False, None== we don't know).

Field.Access can take advantage of those optimizations by making it a subclass of TypedSymbol.

Extended Changes

By writing a test I realized that it would be handy to compare AssignmentCollections and use the functions find, match, subs, replace of SymPy.

pystencils/assignment.py

@@ -49,6 +49,17 @@ else:
         __str__ = assignment_str
         _print_Assignment = print_assignment_latex
 
+# Apparently, in SymPy 1.4 Assignment.__hash__ is not implemented. This has been fixed in current master
+try:
+    sympy_version = sp.__version__.split('.')
+
+    if int(sympy_version[0]) <= 1 and int(sympy_version[1]) <= 4:
+        def hash_fun(self):
+            return hash((self.lhs, self.rhs))
+        Assignment.__hash__ = hash_fun
+except Exception:
+    pass
+
 
 def assignment_from_stencil(stencil_array, input_field, output_field,
                             normalization_factor=None, order='visual') -> Assignment: