scalable < > delimiters in plotmath

Hi

[shifting to r-devel]

On 13/09/2010 8:43 a.m., David Winsemius wrote:

On Sep 12, 2010, at 4:11 PM, Paul Murrell wrote:

Hi

On 13/09/2010 7:57 a.m., baptiste auguie wrote:

Oh, right I see. I was completely off then. Maybe it's not so  
easy to
add<>   delimiters after all, I'll have to look at the list of  
symbol
pieces to see if these can be constructed too.

The plotmath stuff assumes a font with an Adobe Symbol encoding.
The characters we have to play with are shown at http://www.stat.auckland.ac.nz/~paul/R/CM/AdobeSym.pdf
.
You can see the components of "growable" delimiters on the bottom
two rows.

Hello Paul;

Both Baptiste and I have looked at the plotmath.c code and it appears
that only a few of those delimiters are supported. We specifically
have tried to use the angle brackets:

 >  plot(1,1,

xlab=expression(bgroup(symbol(0xe1),atop(x,y),symbol(0xf1))))
Error in bgroup(symbol(225), atop(x, y), symbol(241)) :
   invalid group delimiter

The supported delimiters appear to each be built up from three parts
that are then assembled within a bounding box and as far as I can
determine are limited to "|", "||", "[", "{", "(", ")", "}",and  
"}". I
needed to download the full source to find a copy, but I'm fairly  
sure
a guRu of your standing needs no help finding the code that handles
the bgroup display inside plotmath.c. I am not at my machine where I
was looking at it, but the code that I just found in expanded form on
the Internet bore your name as a copyright holder.

So I guess my feature request would be:
---add option for using scalable single character delimiters such as
Symbol(0xe1) and Symbol(0xe1).

Unfortunately, I don't think this is trivial.  How are these  
supposed to scale?  Just get drawn bigger?  (which is unlikely to  
produce nice results because the lines will get thicker).

I'm guessing that the reason three-component delimiters were chosen  
is
that it was easier to expand the middle section while not expanding
the ends as much but that's just the guess of someone who is perusing
without really being able to fully grasp the intricacies of what is
being done.

That's about right.  This is all modelled on TeX's equation  
formatting algorithms.  The Computer Modern fonts have this kind of  
extendable components for very large delimiters, but for angled  
brackets it looks like the TeX solution is just to offer various  
"big" versions.  For example, try the following TeX document ...

\documentclass{article}
\begin{document}

\[ \left\{
    \begin{array}{ccc}
     a & b & c \\
     a & b & c \\
     a & b & c \\
     a & b & c \\
     a & b & c \\
     a & b & c \\
     a & b & c \\
     d & e & f \end{array}
    \right\} \]

\[ \left\langle
    \begin{array}{ccc}
     a & b & c \\
     a & b & c \\
     a & b & c \\
     a & b & c \\
     a & b & c \\
     a & b & c \\
     a & b & c \\
     d & e & f \end{array}
    \right\rangle \]

\end{document}