[OS X TeX] Vertical space

[Ross Moore]

Hello Alain,

On 25/05/2012, at 9:34 AM, Alain Schremmer wrote:

> Where can I find some information about the way to control vertical space? (I cannot predict the effect of the various commands I use, in particular \\[length]?)

\\[length]  such as  \\[4pt]  adds the *extra* 4pt to what would be the normal
line spacing *within the same paragraph*.

It should *not* be used to place vertical space between paragraphs,
or disparate blocks of text whose content bears little logical relationship 
to each other.

For example:
  .. some random words in one sentence\\[15pt]

  And now a few more words after the blank line


will cause a warning message:    Underfull hbox, badness = 10000
(or similar).

This is because you didn't have any material to finish the paragraph,
following the  \\[15pt] .


The amount of space that this will actually produce is not specified,
cause you have broken the rules concerning 'horizontal' and 'vertical' modes.
Your input is ambiguous, and TeX cannot tell what you really want.

> 
> I have looked in Companion II which does not seem even to mention \\[length], and googled some. I found some interesting sites, e.g. < http://www.maths.tcd.ie/~dwilkins/LaTeXPrimer/WhiteSpace.html> and <http://www.personal.ceu.hu/tex/spacebox.htm> but, that I can see, none mentions \\[length] nor do they quite explain the differences between requiring a particular vertical space, say, after a paragraph, after an item in a list or after a table, etc which I suspect is of the essence.

Within lists, you have the parameter  \itemsep  to specify 
how much space between items.

In tables, there is  \usepackage{tabls}  which defines a length \tablinesep .
This is on p.269 of Companion II.

After a paragraph, your are in "vertical mode".
There are  \smallskip, \medskip, \bigskip  which give increasing amounts 
of space, but are "rubber" lengths which can shrink a bit, if necessary.

Otherwise, you have LaTeX's  \vspace{...}  command, which allows specific
amounts of vertical space.  
BTW, \vspace  is a vertical mode command, so do *not* put it
*inside* a paragraph. It will then migrate to the end of the paragraph,
so the space will not occur where you think it should.

> 
> I am really not asking for an explanation because I can always fudge something so that there is no emergency of any kind but whether anybody knows of some explanation, somewhere because it annoys me having to resort to blind experimentation and not really knowing what I am doing.

Keep your input modular, and within well-defined environments
or paragraphs. If you do this, then there will be few problems,
as LaTeX then has a good idea of your document's structure and 
can translate that internally into the required TeX constructions.

If you want to do other things with the layout, then 
you really need to understand a bit about TeX itself.
e.g. read (at least) chapters 13-15 of The TeXbook
--- maybe 11 & 12 also, concerning boxes and glue.

All of us experiment a bit.
But in my experience, when you don't know what you are doing, 
it is usually because you haven't thought properly about 
the structure inherent in what you are trying to represent
on the page, and the intention of the LaTeX environments that
you are using. 

> 
> Curious regards
> --schremmer


Hope this helps,

	Ross

------------------------------------------------------------------------
Ross Moore                                       ross.moore at mq.edu.au 
Mathematics Department                           office: E7A-419      
Macquarie University                             tel: +61 (0)2 9850 8955
Sydney, Australia  2109                          fax: +61 (0)2 9850 8114
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