[Fix] Printing of subtraction

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):

pystencils_tests/test_print_unsupported_node.py

-# -*- coding: utf-8 -*-
-#
-# Copyright © 2019 Stephan Seitz <stephan.seitz@fau.de>
-#
-# Distributed under terms of the GPLv3 license.
-
-"""
-
-"""
-import pytest
-
-import pystencils
-from pystencils.backends.cbackend import CBackend
-
-
-class UnsupportedNode(pystencils.astnodes.Node):
-
-    def __init__(self):
-        super().__init__()
-
-
-def test_print_unsupported_node():
-    with pytest.raises(NotImplementedError, match='CBackend does not support node of type UnsupportedNode'):
-        CBackend()(UnsupportedNode())

pystencils_tests/test_print_infinity.py → pystencils_tests/test_printing.py

 import pytest
+import sympy as sp
 
 import pystencils
-from sympy import oo
+from pystencils.backends.cbackend import CBackend
+
+
+class UnsupportedNode(pystencils.astnodes.Node):
+
+    def __init__(self):
+        super().__init__()
 
 
 @pytest.mark.parametrize('type', ('float32', 'float64', 'int64'))
@@ -12,9 +19,9 @@ def test_print_infinity(type, negative, target):
     x = pystencils.fields(f'x:  {type}[1d]')
 
     if negative:
-        assignment = pystencils.Assignment(x.center, -oo)
+        assignment = pystencils.Assignment(x.center, -sp.oo)
     else:
-        assignment = pystencils.Assignment(x.center, oo)
+        assignment = pystencils.Assignment(x.center, sp.oo)
     ast = pystencils.create_kernel(assignment, data_type=type, target=target)
 
     if target == pystencils.Target.GPU:
@@ -23,3 +30,24 @@ def test_print_infinity(type, negative, target):
     ast.compile()
 
     print(ast.compile().code)
+
+
+def test_print_unsupported_node():
+    with pytest.raises(NotImplementedError, match='CBackend does not support node of type UnsupportedNode'):
+        CBackend()(UnsupportedNode())
+
+
+@pytest.mark.parametrize('dtype', ('float32', 'float64'))
+@pytest.mark.parametrize('target', (pystencils.Target.CPU, pystencils.Target.GPU))
+def test_print_subtraction(dtype, target):
+    a, b, c = sp.symbols("a b c")
+
+    x = pystencils.fields(f'x: {dtype}[3d]')
+    y = pystencils.fields(f'y: {dtype}[3d]')
+
+    config = pystencils.CreateKernelConfig(target=target, data_type=dtype)
+    update = pystencils.Assignment(x.center, y.center - a * b ** 8 + b * -1 / 42.0 - 2 * c ** 4)
+    ast = pystencils.create_kernel(update, config=config)
+
+    code = pystencils.get_code_str(ast)
+    assert "-1.0" not in code