api: fix Mul arguments processing

Author: mloubout

devito/finite_differences/differentiable.py

@@ -548,20 +548,24 @@ def __new__(cls, *args, **kwargs):
         nested, others = split(args, lambda e: isinstance(e, Mul))
         args = flatten(e.args for e in nested) + list(others)
 
+        # Gather all numbers and simplify
+        nums, others = split(args, lambda e: isinstance(e, (int, float,
+                                                            sympy.Number, np.number)))
+        scalar = sympy.Mul(*nums)
+        try:
+            scalar = sympy.Integer(scalar)
+        except TypeError:
+            pass
+
         # a*0 -> 0
-        if any(i == 0 for i in args):
+        if scalar == 0:
             return sympy.S.Zero
 
         # a*1 -> a
-        args = [i for i in args if i != 1]
-
-        # a*-1 -> a*-1
-        # a*-1*-1 -> a
-        # a*-1*-1*-1 -> a*-1
-        nminus = len([i for i in args if i == sympy.S.NegativeOne])
-        args = [i for i in args if i != sympy.S.NegativeOne]
-        if nminus % 2 == 1:
-            args.append(sympy.S.NegativeOne)
+        if scalar == 1:
+            args = others
+        else:
+            args = [scalar] + others
 
         # Reorder for homogeneity with pure SymPy types
         _mulsort(args)

tests/test_symbolics.py

@@ -8,14 +8,13 @@
 from devito import (Constant, Dimension, Grid, Function, solve, TimeFunction, Eq,  # noqa
                     Operator, SubDimension, norm, Le, Ge, Gt, Lt, Abs, sin, cos,
                     Min, Max, SubDomain)
-from devito.finite_differences.differentiable import SafeInv, Weights
+from devito.finite_differences.differentiable import SafeInv, Weights, Mul
 from devito.ir import Expression, FindNodes, ccode
 from devito.symbolics import (retrieve_functions, retrieve_indexed, evalrel,  # noqa
                               CallFromPointer, Cast, DefFunction, FieldFromPointer,
                               INT, FieldFromComposite, IntDiv, Namespace, Rvalue,
                               ReservedWord, ListInitializer, uxreplace, pow_to_mul,
                               retrieve_derivatives, BaseCast)
-from devito.symbolics.unevaluation import Mul as UnevalMul
 from devito.tools import as_tuple
 from devito.types import (Array, Bundle, FIndexed, LocalObject, Object,
                           ComponentAccess, StencilDimension, Symbol as dSymbol)
@@ -877,16 +876,19 @@ def test_assumptions(self, op, expr, assumptions, expected):
         assert evalrel(op, eqn, assumptions) == expected
 
 
-def test_issue_2577():
+def test_issue_2577a():
 
     u = TimeFunction(name='u', grid=Grid((2,)))
-    eq = Eq(u.forward, UnevalMul(-1, -1., u))
+    x = u.grid.dimensions[0]
+    expr = Mul(-1, -1., x, u)
+    assert expr.args == (x, u)
+    eq = Eq(u.forward, expr)
     op = Operator(eq)
 
     assert '--' not in str(op.ccode)
 
 
-def test_issue_2577a():
+def test_issue_2577b():
     class SD0(SubDomain):
         name = 'sd0'