The problem is that the iterable() function in compatibility thinks
that y is iterable, so it's trying to iterate through y. The fix is to
add IndexedBase to the set of ignored iterables in the function.
Aaron Meurer
On Sat, Jan 25, 2014 at 5:04 AM, Björn Dahlgren <bjo...@gmail.com> wrote:
> Hi!
>
> while using the Indexed class from sympy.tensor I have run into the
> following problem:
>
> cse(...) fails for expressions having "Indexed" instances. They are not
> handled correctly in opt_cse() in cse_main.py
> A possible work-around is to substitute the Indexed instances with dummies,
> perform the CSE elimination and then
> resubstitute the dummies for the indexed symbols. But this is not pretty and
> I think that cse(...) should handle this
> on its own.
>
> Example:
>
> from sympy import *
>
> len_y = 5
> y = IndexedBase('y', shape=(len_y,))
> x = IndexedBase('x', shape=(len_y,))
> Dy = IndexedBase('Dy', shape=(len_y-1,))
> i = Idx('i', len_y-1)
>
> expr1 = (y[i+1]-y[i])/(x[i+1]-x[i])
> expr2 = 1/(x[i+1]-x[i])
> print(cse([expr1, expr2]))
>
> this will cause an infinite recursive call stack to _find_opts raising:
> RuntimeError: maximum recursion depth exceeded in __instancecheck__
>
>
> Does anybody know what the best approach here would be? Add something to the
> Indexed class or modify
> opt_cse?
>
> Best regards
> /Björn
>
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