Re: [eLyXer-users] brackets with \left.

[Jens Nöckel]

Hi Alex,
OK - I've checked out the current version and will look at it some more.
In the meantime, here is what the \left. is supposed to be for:

It allows all brackets to be written in pairs of opening and closing  
type, thus defining an enclosed content. When matching pairs of  
brackets are used on a single line, there is no problem defining the  
enclosed content, but there are situations where you want to define an  
enclosed content while only having a bracket at one end of it. Then  
you use an invisible bracket, represented by \right. or \left.
An important case where this is needed is when the enclosed content  
spans several lines of (say) an eqnarray. The opening bracket - e.g.  
\left{ - is on one line, and the closing \right} on another. LaTeX  
won't be happy unless there is a \right. at the end of the first line  
and a \left. at the beginning of the last. The reason for using  
\left{ in the first place (instead of a plain brace "{" ) is to get a  
bracket whose vertical height is automatically scaled to match the  
content (possibly modified by an additional phantom height). See  
section 18.1.4 (Multiline Brackets) in the LyX Help doc Math.lyx.

The current version of elyxer doesn't seem to have any vertical size  
adjustment of brackets to match, say, enclosed fractions in vertical  
height. So the \left. and \right. constructs really serve no purpose  
here, and one could simply throw them away for now.

Cheers,
Jens


On Dec 13, 2009, at 2:46 PM, Alex Fernandez wrote:

> Hi Jens,
>
> On Sun, Dec 13, 2009 at 9:13 PM, Jens Nöckel <address@hidden>  
> wrote:
> > The reason I'm writing is that elyxer gives wrong HTML output for  
> > brackets
> > such as
> > \left. something \right)
> > where I use the \left. to balance the right bracket with an invisible
> > delimiter. In the HTML output the left delimiter appears as a dot  
> > because
> > the \left tab is recognized as a "onefunction" and immediately  
> > translated by
> > inserting the symbol that follows.
>
> That is just a result of my ignorance of how \left and \right work;
> without knowing any better I just did the minimal work that produced
> acceptable results for the LyX Math manual.
>
> What are they supposed to do? Why is the dot invisible in \left.? Why
> the need to balance a \right with a \left?
>
> > I've looked a little at the code and see a Bracket class, but if I
> > understand correctly it seems to be used only by the pair [ and ],  
> > and it
> > also doesn't leave a trace in the HTML output (i.e., there is no  
> > surrounding
> > <span> in the formula corresponding to the extent of the bracketed  
> > content).
> > But I'm still trying to learn the logic of the code, so correct me  
> > if I'm
> > wrong... Ultimately I think the \left and \right tokens should  
> > count as
> > bracket delimiters, and some way of handling the invisible bracket  
> > for
> > \left. or \right. is needed.
>
> Actually, the Bracket class is just for {} brackets; there is a
> SquareBracket to read [] brackets. Right now none of them have
> anything to do with reading \left and \right commands. A different
> solution should perhaps be found.
>
> > Right now I can fix this by post-processing the HTML do remove the
> > <span class="symbol">.</span>
> > But I'm thinking that the Bracket class is probably the place where  
> > this
> > could be fixed.
>
> Maybe not the Bracket class, but a command is surely the way to go.
> Just be sure to download the source code (not the coalesced
> everything-in-one-big-file elyxer.py) if you want to actually follow
> the code, it is nicely organized in packages:
>  http://www.nongnu.org/elyxer/devguide.html
> and then run eLyXer directly from the source code: instead of
>  $ elyxer.py input.lyx output.html
> run it as
>  $ src/principal.py input.lyx output.html
> I have added an explanation to the developer guide.
>
> Thanks,
>
> Alex.