On Tuesday, 26 September 2017 18:08:07 UTC-4, Aaron Meurer wrote:
>
> For free_symbols, I'm not so sure. It seems to me that the correct
> free_symbols should be {A[i], i}. i is indeed free in the expression.
https://github.com/sympy/sympy/pull/13360
> This is perhaps a bit confusing for Order since it isn't a continuous
> variable, but consider something like a summation.
Now I get:
In [5]: Order(A[i])
Out[5]: O(A[i], A, i, A[i])
I think we need a variation of *free_symbols* that stops at *A[i]* without
going further into *{A, i}*.
> I don't know if it's worth having a separate free_symbols, since
> free_symbols is already a mathematically defined concept.
Well, the question is how to behave in case of composite objects, that is
when you reach an object that is itself a free symbol, but contains other
free symbols inside of it.
The fact
> that a summation or integration variable is not free is a mathematical
> property, not a property of the expression tree. Could we just make it
> so that A[i].free_symbols returns {A[i], i}?
>
We need to make it return *{A[i], A, i} *as *A* may be an array.
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