Documentation for Sum() and Product()

[Martin Fuller]

I was confused by the documentation for sympy.concrete.summations.Sum because it has a long section that uses an exclusive upper bound, but this is not SymPy's style.

It could be improved with a very small change. If the first 4 examples use SymPy's style

  \sum_{i = m}^{n - 1}

instead of Karr's style

  \sum_{m \leq i < n}

then all the text can stay the same. This would be much clearer for people like me who want to understand SymPy, while still being clear for people who understand Karr's summation convention.

Text before the 5th example can then be simplified:

"Note that Karr defines all sums with the upper limit being exclusive, but this does not affect the summation convention. Indeed we have:"

Similar improvements for sympy.concrete.products.Product.

Martin

PS This was reported before but no-one suggested a solution. https://groups.google.com/g/sympy/c/dPm8qkuiu7Y/m/-REDwsUlAgAJ