Ok, that clarifies it a lot.
I will modify the text in order to say that:
- so called « multiply sign » is indeed $\times$, ie ×, and it is pre-break
- with no break there is not such a sign
I would like also to provide an example, maybe the following one looks
more realistic (or less done on purpose) than that given by D. Carlisle.
--8<----8<----8<----8<----8<-- begin -->8---->8---->8---->8---->8----
\documentclass{article}
\begin{document}
Now \(A_3 = 0\), hence the product of all terms \(A_1\) through
\(A_4\), that is \(A_1\* A_2\* A_3 \* A_4\), is equal to zero.
\end{document}
--8<----8<----8<----8<----8<-- end -->8---->8---->8---->8---->8----
The output will look like:
--8<----8<----8<----8<----8<-- begin -->8---->8---->8---->8---->8----
Now A3 = 0, hence the product of all terms A1 through A4 , that is A1 A2 ×
A3 A4, is equal to zero.
--8<----8<----8<----8<----8<-- end -->8---->8---->8---->8---->8----
Maybe we need to @dfn{}-ify the word « discretionary » as this proves
out to be a TeXnical term, add to concept index, and make some short
definition of what it means in general terms. It could be better to
simply make a node \discretionary and refer to it...
V.
Le 27/01/2016 12:22, Johannes Böttcher a écrit :
> Hi
>
> `latex.ltx' shows us the definition:
> \def\*{\discretionary{\thinspace\the\textfont2\char2}{}{}}
>
> Looking up what discretionary means in `texbook.tex`:
>
> \danger A discretionary break consists of three sequences of characters
> called the {\sl pre-break}, {\sl post-break}, and {\sl no-break\/}
> texts. The idea is that if a line break occurs here, the ^{pre-break text}
> will appear at the end of the current line and the ^{post-break text} will
> occur at the beginning of the next line; but if no break occurs, the
> ^{no-break text} will appear in the current line. Users can specify
> ^^|\discretionary|
> discretionary breaks in complete generality by writing
> \begindisplay
> |\discretionary{|\<pre-break text>|}{|\<post-break text>|}{|\<no-break
> text>|}|
> \enddisplay
> where the three texts consist entirely of characters, boxes, and kerns.
> For example, \TeX\ can hyphenate the word
> `difficult' between the f's, even though this requires breaking the
> `ffi' ligature into `f-' followed by an `fi' ligature, if the horizontal
> list contains
> \begintt
> di\discretionary{f-}{fi}{ffi}cult.
> \endtt
> Fortunately you need not type such a mess yourself; \TeX's hyphenation
> algorithm
> works behind the scenes, taking ^{ligatures} apart and putting them
> into discretionary breaks when necessary.
>
>
> \danger A ``^{discretionary multiplication sign}'' is allowed in formulas:
> If you type `|$(x+y)\*(x-y)$|', \TeX\ will treat the ^|\*| something like
> the way it treats \hbox{|\-|}; namely, a line break will be allowed at
> that place, with the hyphenation penalty. However, instead of inserting a
> hyphen, \TeX\ will insert a $\times$ sign in text size.
>
>
>
> \documentclass{article}
> \begin{document}
> \( A \* B \)
> \begin{tabular}{|p{1em}|}
> \( A \* B \)
> \end{tabular}
> \end{document}
>
>
> Wondering about the usefulness, David Carlisle gave another example:
> > pretty sure I have never used it, but basically if you are doing something
> > like group theory with long strings of concatenated symbols for implied
> > multiplication you (might, perhaps) want to allow line breaking but make
> > the multiplication explicit in that case
>
> Johannes
>
>
> On 01/27/2016 10:34 AM, Vincent Belaïche wrote:
>> Hello,
>>
>> In node « Math miscellany », it is mentioned that « \* » produces a
>> « discretionary » multiplication symbol. I tried the following example
>> to see what it looks like (between B and E at the very end of formula):
>>
>> --8<----8<----8<----8<----8<-- begin -->8---->8---->8---->8---->8----
>> \documentclass{article}
>>
>> \begin{document}
>> \[A \times B\times B\times B\times B\times B\times B\times B\times
>> B\times B\times B\times B\times B\times B\times B\times B\times B\times
>> B\times B\times B\times B\times B\times B\times B\times B\times B\times
>> B\times B \* E \]
>> \end{document}
>> --8<----8<----8<----8<----8<-- end -->8---->8---->8---->8---->8----
>>
>> but:
>>
>> - despite the overfull hbox there is not any line break
>>
>> - there is not any explicit multiplication symbol as such between B and
>> E.
>>
>> - not clear what « at which » means, is that immediately _before_ or
>> immediately _after_ the symbol that a line break is allowed
>>
>> Ok « discretionary » means that LaTeX is free to decide about something
>> --- but it is not clear either exactly what is in the discretion of
>> LaTeX, is that to produce or not an explicit symbol, or is that to make
>> or not a line break. As far as I can understand, « discretionary symbol
>> » would mean that the symbol is either produced or not...
>>
>> I made this other experiment:
>>
>> --8<----8<----8<----8<----8<-- begin -->8---->8---->8---->8---->8----
>> \documentclass{article}
>>
>> \begin{document}
>> \noindent\(A \times B\times B\times B\times B\times B\times B\times B\times
>> B\times B\times B\times B\times B\times B\times B\times B\times B\times
>> B\times B\times B\times B \* E \)
>>
>> \noindent\(A \times B\times B\times B\times B\times B\times B\times B\times
>> B\times B\times B\times B\times B\times B\times B\times B\times B\times
>> B\times B\times B\times B\times B \* E \)
>> \end{document}
>> --8<----8<----8<----8<----8<-- end -->8---->8---->8---->8---->8----
>>
>> Here I am using in-line math, not display math, and between the first
>> and the second paragraph there is only one more B factor. There is a
>> line break only in the 2nd paragraph, but not between B and E, and still
>> not any explicit symbol.
>>
>> Any clarification welcome --- impossible to translate something that you
>> can't understand in the first place :-/
>>
>> VBR,
>> Vincent
>>
>>
>
