Updates:
Status: Started
Comment #1 on issue 1434 by ondrej.certik: substitution doesn't work for
sqrt()
http://code.google.com/p/sympy/issues/detail?id=1434
Here is a fix for the sqrt(x*y) problem:
diff --git a/sympy/core/mul.py b/sympy/core/mul.py
index 795b293..f63f805 100644
--- a/sympy/core/mul.py
+++ b/sympy/core/mul.py
@@ -290,7 +290,15 @@ class Mul(AssocOp):
elif coeff < 0:
return (-coeff)**e * Mul(*((S.NegativeOne,)
+rest))**e
else:
- return coeff**e * Mul(*[s**e for s in rest])
+ # we distribute things if all things are positive:
+ if coeff.is_positive:
+ pos = True
+ for s in rest:
+ if not s.is_positive:
+ pos = False
+ break
+ if pos:
+ return coeff**e * Mul(*[s**e for s in
rest])
coeff, rest = b.as_coeff_terms()
Before:
In [1]: sqrt(x*y)
Out[1]:
⎽⎽⎽ ⎽⎽⎽
╲╱ x ⋅╲╱ y
In [2]: x, y = symbols("x y", positive=True)
In [3]: sqrt(x*y)
Out[3]:
⎽⎽⎽ ⎽⎽⎽
╲╱ x ⋅╲╱ y
After:
In [1]: sqrt(x*y)
Out[1]:
⎽⎽⎽⎽⎽
╲╱ x⋅y
In [2]: x, y = symbols("x y", positive=True)
In [3]: sqrt(x*y)
Out[3]:
⎽⎽⎽ ⎽⎽⎽
╲╱ x ⋅╲╱ y
All tests pass, except:
_______________ sympy/series/tests/test_limits.py:test_heuristic
_______________
File "/home/ondrej/repos/sympy/sympy/series/tests/test_limits.py", line
119, in
test_heuristic
assert limit(log(2+sqrt(atan(x)*sin(1/x))), x, 0) == log(2)
File "/home/ondrej/repos/sympy/sympy/series/limits.py", line 79, in limit
r = heuristics(e, z, z0, dir)
File "/home/ondrej/repos/sympy/sympy/series/limits.py", line 98, in
heuristics
return e.subs(e.args[0], heuristics(e.args[0], z, z0, dir))
File "/home/ondrej/repos/sympy/sympy/series/limits.py", line 95, in
heuristics
r.append(a.limit(z, z0, dir))
File "/home/ondrej/repos/sympy/sympy/core/basic.py", line 2139, in limit
return limit(self, x, xlim, direction)
File "/home/ondrej/repos/sympy/sympy/series/limits.py", line 79, in limit
r = heuristics(e, z, z0, dir)
File "/home/ondrej/repos/sympy/sympy/series/limits.py", line 100, in
heuristics
raise PoleError(msg % (e, z, z0, dir))
PoleError: Don't know how to calculate the limit((atan(x)*sin(1/x))**(1/2),
x, 0,
dir=+), sorry.
tests finished: 1438 passed, 4 skipped, 28 xfailed, 1 xpassed, 1
exceptions in 99.56
seconds
DO *NOT* COMMIT!
which is just some small problem in limits, which I'll debug later. This
however
still doesn't fix the subs issue above.
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