Status: Valid
Owner: ----
CC: fred...@witherden.org
Labels: Type-Defect Priority-Medium
New issue 3449 by asmeu...@gmail.com: Autowrap ((x - y)**25).expand() is a
bad example
http://code.google.com/p/sympy/issues/detail?id=3449
This was originally https://github.com/sympy/sympy/issues/1593.
Following the example given in the documentation:
In [1]: from sympy.utilities.autowrap import autowrap
In [2]: from sympy.abc import x,y
In [3]: expr = ((x - y)**(25)).expand()
In [4]: fn = autowrap(expr, language='C', backend='Cython')
In [5]: fn(3, 2)
Out[5]: 0.0
Which is incorrect (subs can be used to trivially show that the correct
result is 1). This is simply a limitation of double precision.
I therefore suggest that something more reasonable is selected given that
the current example may give the (incorrect) impression that the
autowrapping system is broken. Or, better still, use it as an example of a
caveat of using autowrap.
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