Re: multi-symbol variables

On 10/7/21 11:09 PM, David Farmer wrote:
> Taking this discussion out of GitHub.  I hope this is the right
> place.

Seems reasonable.

> The important point which has arisen, which I believe we had not
> discussed previously, is how to mark a multi-letter string as
> representing a single variable.  For example, on this page:

I think we did touch on the issue earlier, but it mostly went under
the radar as other issues got people more excited.

Sometimes, a "complex symbol" (or embellished, or...) can be cast
into the appropriate multi-character mi or mo, possibly using Unicode
tricks of accents, etc.  This would make it a single atomic object,
and it *might* be that this leads to a natural vocalization of it.
But there are many cases where pretty much any MathML layout schema
come into play, sub & superscript, etc, where you can't quite collapse
it into pure Unicode.

Even in that latter case, a vocalization based on a literal readout
might be sufficient; eg "B prime" or "F sub ecks" or whatever.
But if not, we may want to control what is spoken.

And more particularly, independent of how it's vocalized, if there is
some "defaulting" mechanism in play, we need to assert that we *know*
that "B'" is a thing in itself, and that even if we are in a calculus
or chemistry context, that it should *NOT* be matched to a derivative
or isotope or whatever.

So, we need to mark those atomic B' somehow!  It's easy to think of
several extensions to the intent attribute on the <msub>:
* intent="B prime"  : a non-standard intent, so read out as is.
* intent="literal(B prime)" : with literal a keyword: read the argument as is.
* intent="literal"  : a keyword meaning to read out the tree literally.
and probably many more. In all cases, the appearance of such a thing would
preclude descending into the children and applying any "defaulting" rules.
And of course, the keyword could be something other than "literal"...
The key thing in choosing a method is to make sure any keyword (or lack of keyword)
doesn't clash with the eventual dictionary mechanism we choose.

> it says
> Interest = p \times r \times t .
> Here "Interest" is an 8 character string which represents one
> quantity.
> This is analogous to the situation in our recent discussions,
> where B' is just one quantity which happens to be a string of
> two characters.  The fact that one of the characters is a prime
> is not the main issue.  I mentioned an example where a_1 was a
> (subscripted) string which also is really just a single variable.
> Prior to this week I don't think we had discussed the fact that
> B' is a 2-character quantity, while f' -- assuming that means the
> derivative of f -- is the object f on which ' is acting.
> The only point I am trying to make here is that we need a way to
> indicate that a collection of characters is really in indivisible
> unit which represents a single quantity.  The recent discussions were
> made more difficult by the fact that this had not been discussed
> previously.
> I suggest that " B' " should be handled the same way as " Interest "
> would be handled in the formula above.
> Regards,
> David Farmer


Received on Friday, 8 October 2021 13:26:25 UTC