# Re: Subscripts in Content MathML

From: Paul Libbrecht <paul@activemath.org>
Date: Tue, 04 Oct 2005 11:02:37 +0200
Message-ID: <4342452D.9090300@activemath.org>

```
We had similar problems encoding such constructs in OpenMath.
We have found the quick-way: name variables with such names as a_i but
that is definitely not universal.
We know that such an application as a(i) is exactly what we wish the
authors to use but we never managed this completely, one of the reasons
being that aside of the encoding problem of a_i you have such problems
as encoding the ellipsis a_1, ..., a_k, of course, in all flavours such
as with a one removed etc...

Are your authors willing to go that route ? I'd be interested to see a
bit more.
How do you encode content-mathml, btw ?

thanks

paul

Mathematics (General) wrote:
>
> Dear all,
>
> I've got a quick question about the use of subscripts in Content
> MathML which I hope someone can shed some light on.
>
> (a) Background:
>
> Basically, this problem arose with the study of sums; it is often
> useful to describe a summation using a single algebraic letter with a
> subscript denoting the exact term. For example:
>
>    n
> Sum ( a_i ) = a_1 + a_2 + a_3 + ... + a_n
> i = 1
>
> where the a_i notation means "a subscript i". There are lots of
> instances where this notation is used, and I'm sure everyone has come
> across it before; one elementary example is in series (for example,
> see http://mathworld.wolfram.com/Sum.html).
>
> (b) Problem
>
> The MathML spec. suggests than any need for subscripts within Content
> markup should be made using Presentation embedded within Content. For
> example, one way to describe a_i would be:
>
> <ci><msub><mi>a</mi><mi>i</mi></msub></ci>
>
> The problem with this is that the identifiers 'a' and 'i' are
> presentation-only, and hence could not be operated on by our algebraic
> processor engine (which uses a Content-only DOM).
>
> (c) Solution
>
> What we would like to do is the following:
>
> <ci><msub><ci>a</ci><ci>i</ci></msub></ci>
>
> Here we're mixing the two types of mark-up by embedding Content within
> Presentation within Content. However, when the processing engine
> evaluates the sum, it can easily replace all occurances of <ci>i</ci>
> with <cn>1</cn>, <cn>2</cn> etc... which would give the required terms
> (a_1, a_2 etc...) in the sum.
>
> My question is really whether this is VALID mark-up? I believe it
> probably is [DTD definition p.301 MathML 2.0 spec., entities
> %PresExpression and %ContInPres] but I want to make sure with the
> experts that I am correct before proceeding.
>
```
Received on Tuesday, 4 October 2005 10:45:56 UTC

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