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-~----------~----~----~----~------~----~------~--~---
Fix for Mul._eval_subs
Before:
In [2]: (a*b*c).subs(a*c,b)
Out[2]: aâ
bâ
c
After:
In [2]: (a*b*c).subs(a*c,b)
Out[2]:
2
b
diff --git a/sympy/core/mul.py b/sympy/core/mul.py
--- a/sympy/core/mul.py
+++ b/sympy/core/mul.py
@@ -605,28 +605,28 @@
return False
def _eval_subs(self, old, new):
- if self==old:
+ if self == old:
return new
if isinstance(old, FunctionClass):
return self.__class__(*[s.subs(old, new) for s in self.args ])
- coeff1,terms1 = self.as_coeff_terms()
- coeff2,terms2 = old.as_coeff_terms()
- if terms1==terms2: # (2*a).subs(3*a,y) -> 2/3*y
- return new * coeff1/coeff2
- l1,l2 = len(terms1),len(terms2)
+ coeff_self,terms_self = self.as_coeff_terms()
+ coeff_old,terms_old = old.as_coeff_terms()
+ if terms_self == terms_old: # (2*a).subs(3*a,y) -> 2/3*y
+ return new * coeff_self/coeff_old
+ l1, l2 = len(terms_self), len(terms_old)
if l2 == 0:
# if old is just a number, go through the self.args one by one
return Mul(*[x.subs(old, new) for x in self.args])
- elif l2<l1:
+ elif l2 < l1:
# old is some something more complex, like:
# (a*b*c*d).subs(b*c,x) -> a*x*d
# then we need to search where in self.args the "old" is, and then
# correctly substitute both terms and coefficients.
- for i in xrange(l1-l2+1):
- if terms2==terms1[i:i+l2]:
- m1 = Mul(*terms1[:i]).subs(old,new)
- m2 = Mul(*terms1[i+l2:]).subs(old,new)
- return Mul(*([coeff1/coeff2,m1,new,m2]))
+ self_set = set(terms_self)
+ old_set = set(terms_old)
+ if old_set < self_set:
+ ret_set = self_set - old_set
+ return Mul(new, coeff_self/coeff_old, *[s.subs(old, new) for s in ret_set])
return self.__class__(*[s.subs(old, new) for s in self.args])
def _eval_nseries(self, x, x0, n):
diff --git a/sympy/core/tests/test_subs.py b/sympy/core/tests/test_subs.py
--- a/sympy/core/tests/test_subs.py
+++ b/sympy/core/tests/test_subs.py
@@ -130,6 +130,11 @@
assert e.subs(r) == r[a]/r[b] * sin(r[b]*x)
assert e.subs(r) == 3 * sin(4*x) / 4
+def test_mul():
+ x, y, z = map(Symbol, 'xyz')
+ assert (x*y*z).subs(z*x,y) == y**2
+ assert (2*x*y).subs(5*x*y,z) == 2*z/5
+
def test_add():
a, b, c, d, x = abc.a, abc.b, abc.c, abc.d, abc.x
assert (a**2 - b - c).subs(a**2 - b, d) in [d - c, a**2 - b - c]
