Status: Valid
Owner: ----
Labels: Type-Defect Priority-Medium Caching WrongResult
New issue 3969 by sean.v....@gmail.com: Problem with caching and evaluating
derivatives with Dummy's
http://code.google.com/p/sympy/issues/detail?id=3969
The way derivatives are cached causes some problems with evaluating
derivatives. For example:
In [1]: from sympy import Dummy
In [2]: from sympy.abc import a, b, f
In [3]: y1 = Dummy('y')
In [4]: y2 = Dummy('y')
In [5]: func1 = f(a + y1 * b)
In [6]: func2 = f(a + y2 * b)
In [7]: func1_y = func1.diff(y1)
In [8]: func2_y = func2.diff(y2)
In [9]: func1_y == func2_y
Out[9]: True
Since func1 and func2 use different Dummy variables, their derivatives
should differ. Disabling the cache fixes this behavior.
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