Re[3]: Vertical alignment of formulas

[Giuseppe Bilotta <gip.bilotta@iol.it>]

>>Hans, that is *not* supposed to work in those cases because a
>>\par or an empty line determine an end-of-paragraph, so the
>>formula starts a new paragraph and the lenght of the previous
>>line is *irrelevant* --you don't have a mid-paragraph display.
>>
>>I know that you like those freeform spacey sources, but they
>>are not really 100% compatible with the empty line => paragraph
>>concept of TeX :)

Thursday, September 18, 2003 Hans Hagen wrote:

> well, the problem is that in both cases:

>    text $$math$$ text

>    text \par $$math$$ \par text

> one wants to optimize spacing, so the limitation of not having access to
> the last line length is a pitty (i understand that it can be tricky in
> cases like:

>    text \par somevboxmanipulation $$math$$

> since then one may wonder what the last line length applies to

The point is that it's not true that in both cases one wants to
optimize spacing because the two cases have a totally different
meaning: in the first case you have a displayed equation within
a paragraph, so it makes sense to "optimize spacing" to put the
text and the formula as close together as possible (within
aesthetical limits). In the second case you have a formula
which is on a paragraph of its own, and is therefore "absolute"
from the surrounding text. In this case you *don't* want to put
the formula and text as close together as possible because they
are (supposedly) logically *independent* concepts and having
them more spaced in the printout helps noticing this
difference.

In the end it always end up on the totally different views on
displayed material that you and TeX have. We discussed this for
the "autoindent" stuff, remember? You always consider displays
a "separate entity" from the surrounding text, whereas TeX
allows it to be separate or not (depending on \pars around it).
TeX approach is both more flexible and more "correct".

Let's say for example that we're discussing Einstein's
equation. The following three examples have different logical
meaning and should therefore be formatted appropriately
differently:

=== EXAMPLE 1: Display part of the paragraph ===

Einstein's equation $$E=mc^2$$ ties energy and mass of a body
to etc

=== EXAMPLE 2: Display part of the previous paragraph but not
    of the following one ===

A relation between mass and energy of a body is expressed by
Einstein's equation $$E=mc^2.$$

We shall see further on that etc

=== EXAMPLE 3: Display part of the following paragraph but not
    of the previous one ===

some text etc.

$$E=mc^2$$ is Einstein equation and it ties energy and mass
of a body etc.

================================================

In Ex1, you want the displayed equation to have as little
spacing as possible both above and below, and the following
text should NOT start with an indent.

In Ex2, you want the displayed equation to be as close as
possible to the previous text, and to have some spacing below,
to ensure that it's clearly distinguishable from the next
paragraph, which is a new entity. Also, the following text
should start with an indent.

In Ex3, you want there to be more space above than below
because the previous text is independent from the equation. On
the contrary, it should be close together with the following
text which is in the same paragraph as the equation. The
following text should NOT be indented.

Now, while we solved the indenting issue with the introduction
of the indentnext=auto key=value, which automatically takes
care of the various cases, you now have to convince yourself
that the same must hold true for spacing around displayed
material:

text $$math$$ text

and

text\par $$math$$\par text

are NOT the same thing and should be treated differently!

-- 
Giuseppe "Oblomov" Bilotta