clean up pre-existing sign irregularities

without this, it takes multiple pass (4) to resolve sign issues in the `q` expression in the test.
oscargus · Nov 28, 2021 · 74973b0 · 74973b0
1 parent 5e55c1b
commit 74973b0
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diff --git a/sympy/polys/tests/test_polytools.py b/sympy/polys/tests/test_polytools.py
@@ -71,9 +71,10 @@
 from sympy.functions.elementary.miscellaneous import sqrt
 from sympy.functions.elementary.piecewise import Piecewise
 from sympy.functions.elementary.trigonometric import sin
-from sympy.matrices.dense import Matrix, eye
+from sympy.matrices.dense import Matrix
 from sympy.matrices.expressions.matexpr import MatrixSymbol
 from sympy.polys.rootoftools import rootof
+from sympy.simplify.simplify import signsimp
 from sympy.utilities.iterables import iterable
 
 from sympy.testing.pytest import raises, warns_deprecated_sympy
@@ -3088,12 +3089,42 @@ def test_cancel():
     assert cancel((x**2 - 1)/(x + 1) + p3) == (x - 1) + p4
 
     # issue 4077
-    n = -1 + 1/x
-    z = n/x/(-n)**2 - 1/n/x
-    # z is zero so it's derivative should be zero
-    zd = z.diff()
-    assert zd != 0  # if it is, use the explicit expression
-    assert cancel(zd) == 0
+    q = S('''(2*1*(x - 1/x)/(x*(2*x - (-x + 1/x)/(x**2*(x - 1/x)**2) - 1/(x**2*(x -
+        1/x)) - 2/x)) - 2*1*((x - 1/x)/((x*(x - 1/x)**2)) - 1/(x*(x -
+        1/x)))*((-x + 1/x)*((x - 1/x)/((x*(x - 1/x)**2)) - 1/(x*(x -
+        1/x)))/(2*x - (-x + 1/x)/(x**2*(x - 1/x)**2) - 1/(x**2*(x - 1/x)) -
+        2/x) + 1)*((x - 1/x)/((x - 1/x)**2) - ((x - 1/x)/((x*(x - 1/x)**2)) -
+        1/(x*(x - 1/x)))**2/(2*x - (-x + 1/x)/(x**2*(x - 1/x)**2) - 1/(x**2*(x
+        - 1/x)) - 2/x) - 1/(x - 1/x))*(2*x - (-x + 1/x)/(x**2*(x - 1/x)**2) -
+        1/(x**2*(x - 1/x)) - 2/x)/x - 1/x)*(((-x + 1/x)/((x*(x - 1/x)**2)) +
+        1/(x*(x - 1/x)))*((-(x - 1/x)/(x*(x - 1/x)) - 1/x)*((x - 1/x)/((x*(x -
+        1/x)**2)) - 1/(x*(x - 1/x)))/(2*x - (-x + 1/x)/(x**2*(x - 1/x)**2) -
+        1/(x**2*(x - 1/x)) - 2/x) - 1 + (x - 1/x)/(x - 1/x))/((x*((x -
+        1/x)/((x - 1/x)**2) - ((x - 1/x)/((x*(x - 1/x)**2)) - 1/(x*(x -
+        1/x)))**2/(2*x - (-x + 1/x)/(x**2*(x - 1/x)**2) - 1/(x**2*(x - 1/x)) -
+        2/x) - 1/(x - 1/x))*(2*x - (-x + 1/x)/(x**2*(x - 1/x)**2) - 1/(x**2*(x
+        - 1/x)) - 2/x))) + ((x - 1/x)/((x*(x - 1/x))) + 1/x)/((x*(2*x - (-x +
+        1/x)/(x**2*(x - 1/x)**2) - 1/(x**2*(x - 1/x)) - 2/x))) + 1/x)/(2*x +
+        2*((x - 1/x)/((x*(x - 1/x)**2)) - 1/(x*(x - 1/x)))*((-(x - 1/x)/(x*(x
+        - 1/x)) - 1/x)*((x - 1/x)/((x*(x - 1/x)**2)) - 1/(x*(x - 1/x)))/(2*x -
+        (-x + 1/x)/(x**2*(x - 1/x)**2) - 1/(x**2*(x - 1/x)) - 2/x) - 1 + (x -
+        1/x)/(x - 1/x))/((x*((x - 1/x)/((x - 1/x)**2) - ((x - 1/x)/((x*(x -
+        1/x)**2)) - 1/(x*(x - 1/x)))**2/(2*x - (-x + 1/x)/(x**2*(x - 1/x)**2)
+        - 1/(x**2*(x - 1/x)) - 2/x) - 1/(x - 1/x))*(2*x - (-x + 1/x)/(x**2*(x
+        - 1/x)**2) - 1/(x**2*(x - 1/x)) - 2/x))) - 2*((x - 1/x)/((x*(x -
+        1/x))) + 1/x)/(x*(2*x - (-x + 1/x)/(x**2*(x - 1/x)**2) - 1/(x**2*(x -
+        1/x)) - 2/x)) - 2/x) - ((x - 1/x)/((x*(x - 1/x)**2)) - 1/(x*(x -
+        1/x)))*((-x + 1/x)*((x - 1/x)/((x*(x - 1/x)**2)) - 1/(x*(x -
+        1/x)))/(2*x - (-x + 1/x)/(x**2*(x - 1/x)**2) - 1/(x**2*(x - 1/x)) -
+        2/x) + 1)/(x*((x - 1/x)/((x - 1/x)**2) - ((x - 1/x)/((x*(x - 1/x)**2))
+        - 1/(x*(x - 1/x)))**2/(2*x - (-x + 1/x)/(x**2*(x - 1/x)**2) -
+        1/(x**2*(x - 1/x)) - 2/x) - 1/(x - 1/x))*(2*x - (-x + 1/x)/(x**2*(x -
+        1/x)**2) - 1/(x**2*(x - 1/x)) - 2/x)) + (x - 1/x)/((x*(2*x - (-x +
+        1/x)/(x**2*(x - 1/x)**2) - 1/(x**2*(x - 1/x)) - 2/x))) - 1/x''',
+        evaluate=False)
+    assert cancel(q, _signsimp=False) == -1/(2*x)
+    assert q.subs(x, 2) is S.NaN
+    assert signsimp(q) is S.NaN
 
     # issue 9363
     M = MatrixSymbol('M', 5, 5)

diff --git a/sympy/simplify/simplify.py b/sympy/simplify/simplify.py
@@ -402,7 +402,9 @@ def signsimp(expr, evaluate=None):
     expr = sympify(expr)
     if not isinstance(expr, (Expr, Relational)) or expr.is_Atom:
         return expr
-    e = sub_post(sub_pre(expr))
+    # get rid of an pre-existing unevaluation regarding sign
+    e = expr.replace(lambda x: x.is_Mul and -(-x) != x, lambda x: -(-x))
+    e = sub_post(sub_pre(e))
     if not isinstance(e, (Expr, Relational)) or e.is_Atom:
         return e
     if e.is_Add:
@@ -412,7 +414,7 @@ def signsimp(expr, evaluate=None):
             return Mul(S.NegativeOne, -rv, evaluate=False)
         return rv
     if evaluate:
-        e = e.xreplace({m: -(-m) for m in e.atoms(Mul) if -(-m) != m})
+        e = e.replace(lambda x: x.is_Mul and -(-x) != x, lambda x: -(-x))
     return e