On Wed, Oct 20, 2021 at 2:24 PM David Bailey <d...@dbailey.co.uk> wrote:
>
> On 20/10/2021 12:36, Oscar Benjamin wrote:
>
> On Tue, 19 Oct 2021 at 20:55, David Bailey <d...@dbailey.co.uk> wrote:
>
> Dear group,
>
> First I would like to say how good it was to discover that the online
> SymPy documentation now supports copy/paste operations without
> constantly switching to SymPyLive. I think this will make the
> documentation considerably more user friendly.
>
> I'm not sure what has changed there...
>
> Thanks for replying Oscar. You are right! When I went to the SymPy
> documentation to prepare the second part of this email I found it behaved in
> the same old way - maybe the live shell was down last night. The problem is
> that if you click into a block of SymPy code with the intention of cutting
> and pasting its contents, it fires up the live shell when you don't want it -
> at least using Firefox on Windows 10. To cut and paste you have to use a
> trick - clicking outside the block with the green background and dragging
> into the block from there. Since there is a dark green tag above each section
> to invoke the live shell, all that is needed is to disable special trapping
> the left mouse click.
>
> My question is what construct should I use to get variables with
> subscripts, and maybe superscripts. I thought at first that indexed
> objects were the way to go, but they seem rather obscure. E.g. think of
> indexing through the Bessel functions - J0, J1,J2 etc.
>
> Ideally I'd like to loop over the index/indices and also see the
> subscripts positioned below the main symbol when using Latex output
>
> I'm not completely sure what you want here but is this it:
>
> In [19]: symbols('x:10')
> Out[19]: (x₀, x₁, x₂, x₃, x₄, x₅, x₆, x₇, x₈, x₉)
>
> IndexedBase is for the situation where you want the index to be symbolic e.g.:
>
> In [27]: xi = IndexedBase('x')
>
> In [28]: n, m = symbols('n, m')
>
> In [29]: Sum(xi[n], (n, 1, m))
>
> It was the second facility that I was looking for. What fooled me was that in
> the documentation:
>
> https://docs.sympy.org/latest/modules/tensor/indexed.html
>
> The index variables are created specially:
>
> i, j = symbols('i j', cls=Idx)
>
> However it would seem you can index with any integer variable. What does the
> Idx class contribute?
Idx lets you specify a range of values. I think it is also handled
better by the code printers. If you don't need any of those features,
just using a Symbol should work fine.
Aaron Meurer
>
> David
>
>
>
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