[Fix] Printing of subtraction

Subtraction is realised in SymPy with a multiplication of -1 and an addition. Since the -1 is casted in our typing system, it remains in the printer. This leads to many unnecessary number prints. We can avoid this by not casting the negative one

pystencils/typing/leaf_typing.py

@@ -6,6 +6,7 @@ import numpy as np
 
 import sympy as sp
 from sympy import Piecewise
+from sympy.core.numbers import NegativeOne
 from sympy.core.relational import Relational
 from sympy.functions.elementary.piecewise import ExprCondPair
 from sympy.functions.elementary.trigonometric import TrigonometricFunction, InverseTrigonometricFunction
@@ -228,6 +229,15 @@ class TypeAdder:
             new_func = expr.func(*new_args) if new_args else expr
             return CastFunc(new_func, collated_type), collated_type
         elif isinstance(expr, (sp.Add, sp.Mul, sp.Abs, sp.Min, sp.Max, DivFunc, sp.UnevaluatedExpr)):
+            # Subtraction is realised a multiplication with -1 in SymPy. Thus we exclude the coefficient in this case
+            # and resolve the typing entirely with the expression itself
+            if isinstance(expr, sp.Mul):
+                c, e = expr.as_coeff_Mul()
+                if c == NegativeOne():
+                    args_types = self.figure_out_type(e)
+                    new_args = [NegativeOne(), args_types[0]]
+                    return expr.func(*new_args, evaluate=False), args_types[1]
+
             args_types = [self.figure_out_type(arg) for arg in expr.args]
             collated_type = collate_types([t for _, t in args_types])
             if isinstance(collated_type, PointerType):