Added NoEvaluationPiecewise.

This is a sympy.Piecewise wrapper that sets evaluate=False to avoid
expensive simplifications during the kernel generation.

pystencils/backends/cbackend.py

@@ -263,6 +263,9 @@ class CustomSympyPrinter(CCodePrinter):
         result = super(CustomSympyPrinter, self)._print_Piecewise(expr)
         return result.replace("\n", "")
 
+    def _print_NoEvaluationPiecewise(self, expr):
+        return self._print_Piecewise(expr)
+
     def _print_Function(self, expr):
         infix_functions = {
             bitwise_xor: '^',

pystencils/sympyextensions.py

@@ -580,3 +580,10 @@ def sort_assignments_topologically(assignments: Sequence[Assignment]) -> List[As
 class SymbolCreator:
     def __getattribute__(self, name):
         return sp.Symbol(name)
+
+
+class NoEvaluationPiecewise(sp.Piecewise):
+    def __new__(cls, *args, **kwargs):
+        kwargs['evaluate'] = False
+        obj = super(NoEvaluationPiecewise, cls).__new__(cls, *args, **kwargs)
+        return obj