I'm affraid I'm too late already, but I'm sending this anyway. The
lines you sent as an example have two pecculiarities:
- bad alignment
- too short arrows
I managed to solve the first problem -- alignment (with some
"cheating", using TeXBOOK), but I have no idea how to extend
\downharpoonright for example and \longrightleftharpoons also don't
look as they should.
In plain TeX it is possible to say \big\downarrow or \Bigg\downarrow
and the arrow is as long as desired. I neither do understand how this
mechanism works nor did I found out how \downharpoonright was defined
(which font, ...).
Does any Font/TeXnician have any idea how to make \Big\updownharpoons work?
xiaojf said this at Sat, 14 May 2005 21:36:45 +0800:
>
> Hi,
> I can code the cycle in ConTeXt,but it's too ugly and I will try to
> improve it.
> here is my code:
>
> \starttext
> \placeformula
> \startformula
> \matrix{A+B&{\Delta G_1\atop\rightleftharpoons}&AB\cr
> \Delta G_3\!\!\upharpoonleft\!\downharpoonright&&
> \upharpoonleft\!\downharpoonright\!\!\Delta G_4\cr
> A'+B&{\rightleftharpoons\atop\Delta G_2}&A'B\cr}
> \stopformula
> \stoptext
see below
> There is a similar example in "The TeXbook"(example 18.46).
> You can try the follow code:
>
> $$\def\normalbaselines{\baselineskip20pt\lineskip3pt \lineskiplimit3pt }
these are just a few local space adjustment, not important to
undestand the content.
> \def\mapright#1{\smash{
> \mathop{\longrightarrow}\limits^{#1}}}
define a command \mapright:
- \mathop makes \longrightarror behave in a similar way as big
operators like \sum, \int, ...
- \limits makes the ^{#1} appear centered above the arrow smaller than
the rest (the same as super/sub-scripts)
> \def\mapdown#1{\Big\downarrow
> \rlap{$\vcenter{\hbox{$\scriptstyle#1$}}$}}
define a command \mapdown:
- \Big makes the \downarrow longer (no idea how to make something
similar for a harpoon)
- \rlap places the argument to the right of the arrow with virtual box
width 0 (so that the arrow can be centered)
- $\vcenter{\hbox{...}}$ takes care of vertical centering
- $\scriptstyle #1$ is a compensation for ^{#1} above and takes care
that the argument becomes "smaller". Note that if equation is not
typeset in \displaystyle, than it may be that this is not of the same
size as the argument in \mapright
> \matrix{&&&&&&0\cr
> &&&&&&\mapdown{}\cr
> 0&\mapright{}&{\cal O}_C&\mapright\iota&
> \cal E&\mapright\rho&\cal L&\mapright{}&0\cr
> &&\Big\Vert&&\mapdown\phi&&\mapdown\psi\cr
> 0&\mapright{}&{\cal O}_C&\mapright{}&
> \pi_*{\cal O}_D&\mapright\delta&
> R^1f_*{\cal O}_V(-D)&\mapright{}&0\cr
> &&&&&&\mapdown{\theta_i\otimes\gamma^{-1}}\cr
> &&&&&&\hidewidth R^1f_*\bigl({\cal O}
> _V(-iM)\bigr)\otimes\gamma^{-1}\hidewidth\cr
> &&&&&&\mapdown{}\cr
> &&&&&&0\cr}$$
>
> Since i'm just a newbie of TeX, I don't really understand the first a few
> lines
> of the solution. I still need some learning and practice :)
I hope I explained at least a little bit of it.
So here's my proposal (not perfect yet):
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usemodule[nath]
% is there any other way to use local variables than \unprotect?
% I also had to define [EMAIL PROTECTED] once more, which is not very elegant,
% but I don't know any other way
\unprotect
[EMAIL PROTECTED]
% The TeXBOOK, page 358, modified \longrightarrow
% for some reason, the harpoon and line are not 100% perfectly joined
\def\longrightharpoonup{\relbar\joinrel\rightharpoonup}
\def\longleftharpoondown{\leftharpoondown\joinrel\relbar}
% slightly longer line which didn't work: it this looks ugly
% probably a definition, similar as in \overrightarrow
% would help producing longer harpoons
%
% \def\longrightharpoonup{\relbar\joinrel\relbar\joinrel\rightharpoonup}
% \def\longleftharpoondown{\leftharpoondown\joinrel\relbar\joinrel\relbar}
% The TeXBOOK, page 361m modified \rightleftharpoons
[EMAIL PROTECTED]
[EMAIL PROTECTED]@th\hbox{\ooalign{\raise2pt
\hbox{$#1\longrightharpoonup$}\crcr $#1\longleftharpoondown$}}}}
% copied from your code
\def\updownharpoons{\upharpoonleft\!\downharpoonright}
% here are four different placements of \Delta G_i,
% based on Knuth's example above
%
% I tried to explain the command already above
% please ask if there is something you don't understand yet
%
\def\MyEquivTop#1{\smash{\mathop{\longrightleftharpoons}\limits^{#1}}}
\def\MyEquivBot#1{\smash{\mathop{\longrightleftharpoons}\limits_{#1}}}
\def\MyEquivLft#1{\llap{$\vcenter{\hbox{$\scriptstyle{#1}$}}$}\updownharpoons}
\def\MyEquivRt#1{\updownharpoons\rlap{$\vcenter{\hbox{$\scriptstyle{#1}$}}$}}
\protect
$$
% copied from the Knuth's example above
\def\normalbaselines{\baselineskip20pt\lineskip10pt\lineskiplimit10pt}
\matrix{A+B & \MyEquivTop{\Delta G_1} & AB \cr
\MyEquivLft{\Delta G_3} & & \MyEquivRt{\Delta G_4} \cr
A'+B' & \MyEquivBot{\Delta G_2} & A'B \cr}
$$
\stoptext
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Mojca
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