getting metafun positions within (displayed) math mode

getting metafun positions within (displayed) math mode

[Sanjoy Mahajan]

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Dear ConTeXters,

For my sins, and to make students unhappy all over the world, I am
writing another book: _A Student's Guide to Newton's Laws of Motion_
(for Cambridge University Press, aka CUP).  As partial compensation, I
convinced CUP that I may typeset it in ConTeXt and deliver them PDF.

Being hopefully a guide actually useful to students, it will annotate
every symbol in important equations, a feature cribbed from the first
book of the _Student's Guide_ series, Dan Fleisch's _A Student's Guide
to Maxwell's Equations_.

I've attached an image of what such an annotated equation looks like
(from page 2 of Fleisch's book).  It's like a labeled part diagram (say,
for a laptop), where each part (here, each symbol) is connected with an
line to its explanation.

I'm trying to do so with a combination of ConTeXt, MetaPost/MetaFun,
TikZ, and whatever else might work.  But I am a bit stuck at the
following spot.

My plan is to use MetaFun to get the coordinates of each symbol in a
(displayed) equation and then, with MetaFun, connect those symbols to
mini-paragraphs of explanation that surround the equation.

But I am stuck on how to use \hpos in math mode. I'd like to do
something like:

\startformula
\hpos{n1}{\sum}_{\hpos{n2}{0}}^{\hpos{n3}{1}}
\stopformula

to get the locations of the nodes n1, n2, and n3 without interfering
with the math typesetting -- e.g., the engine should still know that
\sum is in display-math mode, so it should be large and have its sub-
and super-scripts below and above it, rather than next to it.

However, the \hpos hides its argument in an \hbox, and thus hides it
from the math layout.  Thus, I have to do something like this minimal
example:

\starttext
\startformula
  \sum_0^1                      % what it should look like
  \quad
  \hpos{n1}{$\displaystyle\sum$}_{\hpos{n2}{$0$}}^{\hpos{n3}{$1$}}
\stopformula
\stoptext

The hpos'ed version after the \quad looks different, even after the
\displaystyle hack.

Is there a version of \hpos for math mode?  That would be the cleanest
solution, because who knows what else would be needed for other cases,
even if the limits can be placed correctly.

Or is there a better way to annotate equations?

(TikZ seems to have the same issue, in that it cannot see into equations.)

Regards,
-- 
-Sanjoy

<http://savelongwharfpark.org/>
Save Long Wharf Park in Boston Harbor!

<http://streetfightingmath.com/>
Six reasoning tools to make hard problems easy.


[-- Attachment #2: example of an annotated equation --]
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[-- Attachment #3: Type: text/plain, Size: 492 bytes --]

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Re: getting metafun positions within (displayed) math mode

[Nigel King]

Wow. I learnt about Maxwell's Equation 48 years ago. I never understood it then nor on the intervening time despite sometimes helping design antennas. The picture and its annotation definitely helps creating clarity. For my twopenneth the effort is very worthwhile.

Thanks

---
Nigel King
Mob: +44 7917 803879
Work:+44 1364 655516


> On 16 Nov 2017, at 21:10, Sanjoy Mahajan <sanjoy@olin.edu> wrote:
> 
> Dear ConTeXters,
> 
> For my sins, and to make students unhappy all over the world, I am
> writing another book: _A Student's Guide to Newton's Laws of Motion_
> (for Cambridge University Press, aka CUP).  As partial compensation, I
> convinced CUP that I may typeset it in ConTeXt and deliver them PDF.
> 
> Being hopefully a guide actually useful to students, it will annotate
> every symbol in important equations, a feature cribbed from the first
> book of the _Student's Guide_ series, Dan Fleisch's _A Student's Guide
> to Maxwell's Equations_.
> 
> I've attached an image of what such an annotated equation looks like
> (from page 2 of Fleisch's book).  It's like a labeled part diagram (say,
> for a laptop), where each part (here, each symbol) is connected with an
> line to its explanation.
> 
> I'm trying to do so with a combination of ConTeXt, MetaPost/MetaFun,
> TikZ, and whatever else might work.  But I am a bit stuck at the
> following spot.
> 
> My plan is to use MetaFun to get the coordinates of each symbol in a
> (displayed) equation and then, with MetaFun, connect those symbols to
> mini-paragraphs of explanation that surround the equation.
> 
> But I am stuck on how to use \hpos in math mode. I'd like to do
> something like:
> 
> \startformula
> \hpos{n1}{\sum}_{\hpos{n2}{0}}^{\hpos{n3}{1}}
> \stopformula
> 
> to get the locations of the nodes n1, n2, and n3 without interfering
> with the math typesetting -- e.g., the engine should still know that
> \sum is in display-math mode, so it should be large and have its sub-
> and super-scripts below and above it, rather than next to it.
> 
> However, the \hpos hides its argument in an \hbox, and thus hides it
> from the math layout.  Thus, I have to do something like this minimal
> example:
> 
> \starttext
> \startformula
>  \sum_0^1                      % what it should look like
>  \quad
>  \hpos{n1}{$\displaystyle\sum$}_{\hpos{n2}{$0$}}^{\hpos{n3}{$1$}}
> \stopformula
> \stoptext
> 
> The hpos'ed version after the \quad looks different, even after the
> \displaystyle hack.
> 
> Is there a version of \hpos for math mode?  That would be the cleanest
> solution, because who knows what else would be needed for other cases,
> even if the limits can be placed correctly.
> 
> Or is there a better way to annotate equations?
> 
> (TikZ seems to have the same issue, in that it cannot see into equations.)
> 
> Regards,
> -- 
> -Sanjoy
> 
> <http://savelongwharfpark.org/>
> Save Long Wharf Park in Boston Harbor!
> 
> <http://streetfightingmath.com/>
> Six reasoning tools to make hard problems easy.
> 
> <annotated-equation.png>
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to the Wiki!
> 
> maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
> archive  : https://bitbucket.org/phg/context-mirror/commits/
> wiki     : http://contextgarden.net
> ___________________________________________________________________________________


___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : http://contextgarden.net
___________________________________________________________________________________

Re: getting metafun positions within (displayed) math mode

[Aditya Mahajan]

On Thu, 16 Nov 2017, Sanjoy Mahajan wrote:

> However, the \hpos hides its argument in an \hbox, and thus hides it
> from the math layout.  Thus, I have to do something like this minimal
> example:
>
> \starttext
> \startformula
>  \sum_0^1                      % what it should look like
>  \quad
>  \hpos{n1}{$\displaystyle\sum$}_{\hpos{n2}{$0$}}^{\hpos{n3}{$1$}}
> \stopformula
> \stoptext
>
> The hpos'ed version after the \quad looks different, even after the
> \displaystyle hack.
>
> Is there a version of \hpos for math mode?  That would be the cleanest
> solution, because who knows what else would be needed for other cases,
> even if the limits can be placed correctly.
>
> Or is there a better way to annotate equations?

No time for a detailed answer, but what you need is the following:

\starttext
\startformula
   \sum_0^1                      % what it should look like
   \quad
   \mathop{\hpos{n1}{\mathsurround\zeropoint$\displaystyle\sum$}}_{\hpos{n2}{\mathsurround\zeropoint$\scriptstyle0$}}^{\hpos{n3}{\mathsurround\zeropoint$\scriptstyle1$}}
\stopformula
\stoptext

So what you need to do is find the mathmode of the current symbol 
(mathbin, mathord, etc) and find the mathstyle of the current symbol 
(\displaystyle, \scriptstyle, \scriptscriptstyle, etc), and reapply those.

There is some code in the core to do detect whether the current symbol is 
a bin or not (and perhaps that can be adapted to see if the current symbol 
is an op or not). But a simpler solution will be use luatex to traverse 
the mathlist after it has been typeset (but I don't understand who that 
works).

Of course, an ideal solution will be to define a macro \mpos{...} that 
does this behind the scenes.

Aditya
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___________________________________________________________________________________

Re: getting metafun positions within (displayed) math mode

[Sanjoy Mahajan]

[Sorry for probably breaking the threading -- long story with not using
the mailing-list administrative interface correctly at first.]

Aditya writes:

> No time for a detailed answer, but what you need is the following:
> ...

Thank you -- that should work.  I won't have many of these equation
beasts, and I can annotate them with \mathop, \mathord, etc. without
much trouble.  If I get ambitious, I'll look into the LuaTeX parsing.
But I fear that there aren't enough such equations to force me into
learning that much of the internals.

Maybe there's even an easier way with \mpos creating some kind of
callback, whereby LuaTeX talks back to it after typesetting the math
node?  Perhaps it adds a field to the node tree (if that's the right
word).  But I am rapidly spiraling beyond my LuaTeX understanding...

Nigel King writes:

> Wow. I learnt about Maxwell's Equation 48 years ago. I never
> understood it then nor on the intervening time despite sometimes
> helping design antennas. The picture and its annotation definitely
> helps creating clarity. For my twopenneth the effort is very
> worthwhile.

The _Maxwell's Equations_ book is really good.  I hope that mine can be
two-thirds as good.

-Sanjoy
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : http://contextgarden.net
___________________________________________________________________________________